There are nine different subclasses to choose from in Destiny 2, and in general, they all have very different abilities.
Titans have a ton of variety when it comes to how each subclass does what it does, but all of them can be really effective in Crucible. For this list, let's take a look at the Sentinel subclass, and how to get the most out of it in Crucible:
10 SENTINEL SHIELD
The Sentinel Shield is the supercharge for the Sentinel subclass unless you've chosen the Code of the Commander. The Sentinel Shield equips a Void shield that you can use to block incoming attacks, melee enemies, or throw to kill enemies from afar. Each of these attacks is a one-shot, and you can block just about anything at all with the shield, making this one of, if not the best and most versatile, super in the game as far as Crucible is concerned.
9 GRENADES
The Sentinel subclass has access to the Magnetic Grenade, Voidwall Grenade, and the Suppressor Grenade. Each of these grenades serve a very different purpose, and each of them can be used to a lot of success. The Magnetic Grenade will attach to enemies if thrown accurately enough, and will explode twice, dealing heavy damage and putting enemies on their last legs.
The Voidwall Grenade detonates when it lands on the ground, firing out a wall of Void damage perpendicular from the direction you threw it (unless it hit a wall, then, like, flip a coin or something). This is a decent way to cut off a lane, but it likely isn't going to do terribly heavy damage to enemies that just sprint through it.
The Suppressor grenade is probably the most unique grenade in Destiny 2. It explodes like a normal grenade, and enemies that are in the damage radius take a bit of damage and are unable to use abilities for a short time, too. This is a great grenade for Crucible and can really ruin the day of an enemy that relies heavily on their abilities.
8 MELEE
As with all Titan subclasses, the Sentinels have some pretty nice melee abilities, including one that functions very similar to Seismic Strike. Other than that, melee abilities in the Sentinel subclass have the capability to grant you an overshield on killing as enemy, and creating a Void explosion with your fist. Titans are generally designed around an up-close and personal style, and their melee abilities are no slouch.
7 BARRICADE
All Titans have access to the same two Barricade abilities: Towering Barricade, and Rally Barricade. Towering Barricade gives quite a bit of cover; enough for both you and a couple of allies, as well.
Rally Barricade usually isn't going to be nearly as helpful as the Towering Barricade simply because it doesn't give even close to as much cover, though it does increase reload speed while behind it.
6 LIFT
All Titans have access to the same movement abilities: High Lift, Strafe Lift, and Catapult Lift. High Lift gives you some extra height, but that isn't generally going to be super helpful in Crucible.
Strafe Lift gives you a bit of extra control while in the air, which can go a long way in making sure you aren't an easy target.
The Catapult Lift gives you some extra speed upon lifting, which is very helpful for those that want an up-close-and-personal build.
5 CODE OF THE AGGRESSOR
Code of the Aggressor comes with the abilities Shield Bash, Superior Arsenal, Second Shield, and In The Trenches. Shield Bash is activated the same way Seismic Strike is; sprint for a short time, and it can be activated. Shield Bash comes with the added bonus of disorienting and suppressing enemies, as well.
Superior Arsenal grants grenade energy upon getting a grenade kill, allowing Guardians that are skilled with grenades to have them active more often.
Second Shield grants an additional Shield Throw Charge with the Sentinel Shield active. The Shield Throw is fantastic for Crucible, and this extra shield is going to net you a lot more kills than you might otherwise get.
In The Trenches reduces the cooldown of your super when you get a kill while surrounded by enemies. Being surrounded is, generally, not the best tactic for Crucible, and this ability isn't usually going to be that noticeable.
4 CODE OF THE COMMANDER
Code of the Commander comes with the abilities Banner Shield, Tactical Strike, Resupply, and Controlled Demolition. Banner Shield slightly modifies the Sentinel Shield super, allowing guarding with the shield to create a defensive wall that protects you and allies while granting allies that shoot through the wall increased weapon damage. On a well-coordinated team, this can be a pretty decent super, though usually isn't going to be as destructive to an enemy team as simply smashing them your shield yourself.
Tactical Strike creates a void explosion upon meleeing an enemy. This combined with the later Controlled Demolition can be of decent benefit, for reasons we'll get into in a bit.
Resupply allows you and nearby allies to regain health, grenade, and melee energy when your Void Detonators explode, making constant use of your Void abilities of massive benefit to your entire team.
Controlled Demolition attaches Void Detonators to enemies when you damage them with a Void ability. Causing further damage to an enemy with a Void Detonator attached detonates the detonator.
3 CODE OF THE PROTECTOR
Code of the Protector comes with the abilities Defensive Strike, Rallying Force, Ward of Dawn, and Turn the Tide. Defensive strike creates an overshield around you and nearby allies when you defeat an enemy with your melee. This can be a great way to outlast multiple enemies, further incentivizing close-range combat that keeps the advantage in your favor.
Rallying Force restores a portion of health to you and nearby allies upon a melee kill, which, combined with the above ability, is kind of bonkers.
The only reason the above two abilities aren't completely nuts in Crucible is because Ward of Dawn replaces the Sentinel Shield as your super ability, instead covering you and your immediate surroundings by an impenetrable dome. It also increases weapon damage for you and allies that pass through it. This isn't a great super for Crucible, as it has basically zero kill potential, but can be alright for certain situations.
Turn the Tide allows the overshield granted from Defensive Strike to last longer, and increases mele damage and reload speed. Melee combat with this subclass is truly insane.
2 URSA FURIOSA G
The Ursa Furiousa G exotic armor is a pretty interesting exotic for Crucible. With this armor on, you can move faster while blocking with your Sentinel Shield, and that blocked damage will convert to super energy when your super ends, allowing you to activate your super again in a shorter period of time. This allows you to walk down enemies a bit easier without fear of taking as much damage because you can block while doing so, and helps you get the super active three or four times in a match pretty easily, as opposed to just twice.
1 PUNCH EVERYTHING
The Sentinel subclass, especially the Code of the Protector, revolves around baiting enemies into getting into close-range fights that they are not equipped to beat you in. Playing into that strength can make you a monster in Crucible, and someone enemies are not going to want to have to play against.
For tips on using the Striker subclass, click here. For tips on using the Sunbreaker subclass, click here.