Let's get this out of the way right off the bat: Rainbow Six Siege is a very situational game, and it's very hard to quantify exactly how useful an operator or a tactic is going to be until the round starts. (Or, at least until the preparation phase.) With that said, there are operators in Siege that are going to be useful in a wider variety of situations than others. This list ranks those operators (Attackers and then Defenders) who are useful more often near the top and puts operators who are much more situational towards the bottom. The list has been made from a combination of personal experience and general player opinions. For newer players, you might want to work towards unlocking the more useful operators first, and for the experienced players out there, maybe you'll learn something new! With that said, if you're having success with an operator that's lower on this list, don't let this list stop you!
48 THERMITE (S-TIER)
Most objectives in Rainbow Six Siege are going to be a million times easier to attack if the attacking team has a hard breacher. Thermite is the original hard breacher in Siege, and despite needing to physically attach his gadget onto the wall he wants to breach, he's still a fantastic, and often critical operator to have.
47 HIBANA (S-TIER)
Hibana is the other true hard breacher in Siege, added shortly after launch. Her gadget allows her to open reinforced walls from a distance, and despite having a gun that can be a bit difficult to use because of its low magazine capacity, she remains another great operator pick.
46 THATCHER (S-TIER)
The usually-necessary companion to a hard breacher, Thatcher's gadget allows him to destroy/disrupt any enemy gadget that requires power to run. This includes the often-used Defender gadgets that foil hard breachers, like Bandit's battery, Kaid's electroclaw, and Mute's jammer.
45 MAVERICK (A-TIER)
Maverick is the only other (almost) hard-breacher in Siege. While his gadget can make a hole in a reinforced wall big enough to travel through, it's going to take a bit of time to accomplish, leaving him exposed for quite a while. It's often necessary to have a partner with Maverick watching his back. However, his gadget is also great for other things, like its ability to open unreinforced hatches swiftly, and its ability to destroy Maestro's evil eyes.
44 BUCK (A-TIER)
Buck is probably the best operator for vertical play in all of Siege. His ability to open both floors and ceilings makes him a huge problem for anchors in certain objectives, and on a well-coordinated team, his ability to push anchors out of the spots of relative safety is a difficult thing to counter, provided the enemy roamers are taken care of.
43 SLEDGE (A-TIER)
Sledge is another fantastic choice for soft-breaching/vertical play, and while he can't open ceilings like Buck can, Sledge can use his hammer many more times than Buck can fire his shotgun. If you're certain the objective site is going to be below you, Sledge is arguably a better choice than Buck.
42 ZOFIA (A-TIER)
Zofia has an astronomical amount of utility and versatility, making her a great choice for just about any objective in the game. Her impact grenades allow for incredibly quick soft breaching capability (including vertical play) and her concussion grenades are a great substitute for a drone if you don't have any left, since they explode immediately when near an enemy.
41 ASH (A-TIER)
Everyone's worst nightmare to have running at you, Ash is the primary entry-fragger in Siege, meaning she's usually the operator entering the building first and (hopefully) making quick work of a surprised roamer or two. While not quite as great as Zofia's, Ash's gadget is definitely good, and despite the recent removal of the ACOG from her primary weapon, it's still a beast of a gun.
40 TWITCH (A-TIER)
Despite constant nerfs to her gadget, her drone is still relatively effective at what it's there for: taking out enemy gadgets. While they're nowhere near as effective as they once were, they can still be a good benefit to your team. But where Twitch really shines is her weapon, the F2, which is one of the best weapons in the game.
39 IQ (A-TIER)
IQ is a difficult operator to rank, simply because of how much the enemy team can affect her usefulness. Her gadget allows her to see any enemy gadget that runs on electricity through walls, meaning she shouldn't ever be surprised by most of the gadgets in the game. However, the loss of her frag grenades really hurt her ability to destroy enemy gadgets around corners. That being said, in the current trap-meta we have in Siege, IQ is the perfect solution.
38 CAPITAO (B-TIER)
Capitao is another operator that has a huge amount of utility available to them, what with his crossbow that can either smoke an area or cover it in flames. The only reason he isn't quite in the A-Tier is because of his somewhat lackluster weaponry.
37 JACKAL (B-TIER)
Jackal is one of the best roam-clearing operators out there. His ability to locate and track down any Defender with ease (besides Caveira) is great, and he has some fantastic weaponry. He does, however, require a solid amount of map knowledge to use to his full potential.
36 YING (B-TIER)
If stun effects from flash grenades and Ying's candela worked with any consistency in Siege, Ying would be much higher on this list. However, despite the inconsistency with her gadget, Ying remains a solid choice, because when her gadget works as it should, it's supremely easy to walk into a room full of blinded enemies and get some easy kills.
35 BLACKBEARD (B-TIER)
Blackbeard is another operator that has been the target of quite a few nerfs, albeit many of them were warranted. Though he's a shadow of his former self, Blackbeard is still a real pain to get into a gunfight with, because in any gunfight of equal footing, Blackbeard will come out the victor due to his rifle shield.
34 MONTAGNE (B-TIER)
Montagne is an Attacker that can, on occasion, be quite literally unkillable. His full-body shield allows him to be untouchable by anything but smoke and traps, so there are certain corners he can wedge himself into that don't allow Defenders to do anything at all about him, until Montagne decides differently. With a well-coordinated team, Montagne can be a true force of nature; but without a well-coordinated team, he's all but useless.
33 NOMAD (B-TIER)
Nomad is, perhaps, the operator that can give the enemy roamers the biggest headache. Her airjabs can completely cut off roamers rotation paths, essentially trapping the roamers into an area unless they want to give themselves away. Map knowledge can really make Nomad a difficult operator to deal with, but without the proper map knowledge, her airjabs may be completely wasted.
32 GRIDLOCK (B-TIER)
The only 3-armor Attacker without the option of having a shield, Gridlock more than makes up for it with very good weaponry, including a secondary shotgun that gives her breaching capabilities, and a gadget that allows her to rival Nomad's ability to cover the flank. If you're aren't a fan of Nomad's weapons, Gridlock is a good operator to give a chance.
31 DOKKAEBI (B-TIER)
Dokkaebi would be a lot higher rated if she had a better primary weapon at her disposal. But as it is, Dokkaebi is an operator with a fantastic gadget allowing you to get an unrivaled amount of intel on the enemy team, only lacking in her fragging capabilities. If you happen to be a fan of using semi-automatic weapons in Siege, she's definitely worth giving a chance.
30 NOKK (C-TIER)
While Nokk's gadget can be difficult to use because of the limited time it can be active, when it works, it really works. It allows her to move almost silently and invisible to cameras, giving her ample opportunity to catch enemies completely unaware, though her lack of an ACOG can definitely be a problem, sometimes.
29 LION (C-TIER)
Lion is an operator that used to be wickedly overpowered and has been toned down drastically in order to put him where he probably should be. Lion can be a good choice, and can very much turn the tide in your favor, but in order to make him really make a difference, it requires an incredible amount of coordination with your team and the right situation given to you by the defenders. Most of the time, his gadget is going to give a few seconds of peace, and not much else.
28 BLITZ (C-TIER)
Blitz can absolutely be a force of nature for the Attackers, but it does require a lot things to go in your favor. Most of the time, he's only really going to be effective in a scenario where he's fighting one Defender at a time. Multiple Defenders are likely to gain two different angles on him, thus ruining his day. With a solid teammate(s) coming in behind you, Blitz can be effective as a surprise entry fragger, but the noise his shield creates makes that unlikely to be as effective as a number of different operators.
27 FINKA (C-TIER)
Finka is by no means a useless operator, and her gadget can definitely be a boon to your team, but most of the time the effect her gadget has on a fight in pretty negligible. If coordinated, her gadget can be used to get rid of the concussion effect from Echo's drone of Ela's mines, as well as a couple of other effects. But usually, her gadget just isn't going to sway things one way or another.
26 GLAZ (C-TIER)
Glaz's most recent nerf has severely impacted his ability to do anything, really. In order to get the thermal vision to work (which is necessary to see through smoke grenades) you need to stand perfectly still and wait a couple of seconds. Besides that, his gun really isn't good compared to just about every other option in the game. Glaz can be effective in very, very specific scenarios where you can hold a long sightline and know you aren't going to be hit from a direction you aren't looking in, but opportunities like that are few and far between.
25 FUZE (C-TIER)
Against newer players, Fuze can definitely be an operator worth using, but once you start getting into games against players that have seen a thing or two, the usability of Fuze pretty much drops off the map. If you're using him simply to get rid of enemy gadgets, then you may find some level of success with him. But if you're using him in the hopes to get much in the way of kills with his gadget, you're probably going to be disappointed.
24 BANDIT (S-TIER)
It's no surprise to see Bandit up here. Despite losing his ACOG a long time ago, Bandit has some incredible fragging potential with his great weaponry, and his gadget is a hard breachers worst nightmare. In order to counter enemy Thatcher's, Bandit can deploy his batteries as the Attacker's hard-breachers activate their gadget, destroying them just before they do their work.
23 MAESTRO (S-TIER)
Maestro is often ludicrously undervalued. One of (if not the best) anchor operator in the game, Maestro has an incredible weapon and invaluable gadgets. His evil eye cameras can only be destroyed by a chosen few operators (if placed correctly), and their ability to both give intel and be a constant nuisance to Attackers is very underrated.
22 JAGER (S-TIER)
The last of the S-Tier, Jager makes it up here because his gadget is useful in every single objective site. There are some sites where a Jager is absolutely necessary, but any site is going to benefit from his ordinance-destroying ADS. Aside from that, he has some excellent fragging potential.
21 MIRA (A-TIER)
While not every objective site benefits from having a Mira window (and some objectives can become harder to defend because of them), when a Mira window is useful, it changes the game entirely. A well-placed and well-managed Mira window is an impassable obstacle for Attackers, and it can force them right where you want them to go.
20 VALKYRIE (A-TIER)
Valkyrie is another operator that is great to have on any objective site in the game. Well-placed Valkyrie cameras can be the difference between winning and losing with their ability to give intel from anywhere in the map. The only thing lacking with Valkyrie is her fragging potential.
19 MUTE (A-TIER)
Drones are some of the most valuable objects in the game, and Mute is the greatest counter to the effectiveness of a drone. Well-placed Mute jammers can keep the Attackers from a lot of intel, and that alone can make a humongous difference.
18 LESION (A-TIER)
While not quite as deadly as some of his other trapping friends, Lesion can have just as big of an impact especially the later in the round it gets. As long as the Lesion is paying attention to where each gu mine is when it's triggered and, if necessary, communicating that location, he can make a significant difference.
17 FROST (A-TIER)
While her traps are not nearly as difficult to see as Lesion's (or even Kapkan's), according to the most recent win-delta released by Ubisoft, Frost is severely underpicked and has a very high win delta. When placed well, her traps are an utter nightmare for Attackers, and neither Thatcher nor Twitch can get rid of them with their respective gadgets. The only real counter to Frost is keeping an eye on your footing and droning well.
16 ELA (A-TIER)
Another operator pretty underpicked but still highly-useful is Ela. Though her gun did go through some serious (and needed) nerfs, she's still a very viable operator who has a gadget that can really give you and your teammates the upper hand in fights.
15 KAPKAN (A-TIER)
Once more, an operator who isn't picked very often but can make a big difference in a round is Kapkan. Sure, his traps can be pretty easily spotted by Attackers that are paying attention, but when placed in locations that aren't quite as expected, they can surprise Attackers. Plus, the later the round gets, the less likely an Attacker takes the time to look for the traps, so if you're playing with a couple of solid roamers that waste a lot of the Attackers time, Kapkan can certainly be an effective pick.
14 ECHO (A-TIER)
Echo has absolutely fantastic weaponry, but the reason he's rated so high is because his gadget is crazy valuable. His drones fire something that gives Attackers a concussion effect that not only makes it difficult for them to fight, it also interrupts them while planting. If time is short and the Attackers haven't planted, an Echo's Yokai drone is your best friend.
13 KAID (B-TIER)
While not quite as valuable a Bandit in certain situations, Kaid is still an operator that can make a huge difference in a round, especially when paired with a Bandit/Mute. While his weapons are certainly less good than Bandit's, Kaid has the ability to electrify ceiling hatches, which can make a huge difference in certain objective sites. (Unless the enemy team has a Thatcher)
12 PULSE (B-TIER)
Pulse is an operator that can really throw the Attackers for a loop, but this only really happens if the Pulse has very solid map knowledge and situational awareness. He's one of the most difficult operators to use to his full potential, but a good Pulse can be a huge problem for the enemy team.
11 MOZZIE (B-TIER)
A good gun and a very unique gadget make Mozzie an interesting operator to play. He certainly has strong fragging potential with a good weapon and 3-speed, and his gadget allows for both intel-denial and intel gathering. The downside of this is that Mozzie often can have a lot to do, which can be somewhat overwhelming, especially for newer players.
10 DOC (B-TIER)
An operator that lends themselves to a few different playstyles, Doc can be very effective provided they're given the right situation. A Doc player either needs to have strong gun-skill, allowing them to get some kills while roaming with their gadget gaining them back the health they lost in the fight, or they need to be in the objective giving health and support to any anchors and rotating roamers. Because of the one-shot-headshot mechanic in Siege, Doc can only be so useful.
9 ALIBI (B-TIER)
In objectives/maps that have crucial windows, Alibi is a godsend. Her decoys allow you to block the sightline through the window, denying the Attacker any easy visual and either forcing them inside or into waste a frag grenade. She also has a secondary shotgun-lite and impact grenades, allowing her to open up her own rotation routes, which is invaluable as a 3-speed.
8 ROOK (B-TIER)
With the same decent weapons as Doc, Rook is by default a bit more team-oriented as he can drop armor for teammates to wear. This armor isn't usually going to make much of a difference, but every once in a while it's possible to revive a downed teammate that would have been dead without the armor. As an anchor, Rook isn't a terrible choice.
7 CAVEIRA (B-TIER)
While a coordinated team isn't likely to have issues keeping a Caveira under control, most teams (and newer players) are going to have a lot of trouble dealing with her. While her interrogation isn't something you're likely to get off very often, when it is possible, it immediately shifts the momentum in your team's favor.
6 VIGIL (B-TIER)
Good weaponry saves Vigil from mediocrity. While his gadget doesn't really do a whole lot for him, it does ensure he isn't going to get pre-fired nearly as often as other roaming operators. Plus, his weaponry is solid, giving him a good chance to win most gunfights he's in.
5 CASTLE (C-TIER)
Outside of a coordinated team, or in the hands of a new player, Castle is usually going to end up being a hindrance rather than a help. However, there are certain strategies that are helped by a Castle, and his barricades get more and more valuable the longer a round goes.
4 SMOKE (C-TIER)
Because his gadget works like C4 and isn't a fire-and-forget or even an impact activation, Smoke is rated much lower than a lot of the other trap-operators. While he can be a good counter to shield operators and his gadget can effectively time out a round in the right situation, he's a bit lacking overall.
3 CLASH (C-TIER)
Clash is an operator that looks good on paper, and there's not much worse than having to fight against one. However, nine times out of ten, Clash ends up being a nonfactor, with her shield being an annoyance rather than something to truly worry about.
2 WARDEN (C-TIER)
Choosing Warden, in very certain situations, can make the difference between winning and losing. The problem with Warden (besides his lackluster weaponry) is that it's impossible to know how useful his gadget is going to be until the round is playing out. Most of the time, his glasses just aren't going to come into play.
1 TACHANKA (C-TIER)
We've arrived. Lord Tachanka, as he's been lovably named by the Siege community, can actually be a force to be reckoned with. But, it absolutely needs to be the perfect situation. Teaming him up with a Jager, for example, can make for a fun time, as can (if you're willing to be a little bit toxic) setting his turret up at a window and firing out at the Attackers as they spawn. But at the end of the day, despite his high-powered turret and decent weaponry, Tachanka is destined to be at the bottom.