As the magicians of the Marvel Cinematic Universe, Scarlet Witch and Doctor Strange are crucial members of the Avengers, and the destruction of Thanos would not have been possible without them. Wanda Maximoff and Steven Strange are two sides of the same coin; pursuing a similar purpose while taking vastly different paths.
Doctor Strange is the creator of portals and analyst of the future, with a vast array of powerful magical artifacts at his disposal and a genius-level intellect. However, Scarlet Witch is an impassioned sorceress with intense protective instincts who has lost her brother and her lover to conflict.
So, who is the most powerful character?
To avoid spoilers, the events of Doctor Strange and the Multiverse of Madness will be largely ignored.
Chaos Magic Vs. Eldritch Magic: Scarlet Witch
In the MCU, magic has fewer frills and trimmings and basically boils down to how well energy is manipulated. Eldritch Magic is born from the Masters of the Mystic Arts and relies heavily on one's ability to memorize complicated spells, resulting in tangible energy creation. With multifaceted applications, it takes extensive training to become an accomplished Sorcerer, something even the genius Steven initially struggles with.
Unlike Doctor Strange, Wanda was born with her chaos magic capabilities, therefore having her whole life to hone her skills. Wanda's Chaos Magic received a significant power boost from the Mind Stone, granting Scarlet Witch the aptitude for spontaneous creation and enough energy to take on Thanos single-handedly.
First Class Travel: Doctor Strange
One of Doctor Strange's signature moves is his portal creation abilities, whereby tunnels are carved through space and time for a speedy relocation. These portals can travel throughout the Multiverse, opening passageways to otherwise unreachable dimensions. His mastery of Mirror Dimension Magic enhanced his options significantly, by transporting potentially catastrophic battles to a safer location of an alternate dimension.
Scarlet Witch is capable of teleportation, but it appears to not be her favorite move to rely on. She is seen more often levitating as a means of transport, which is not as speedy or far-reaching as Steven's techniques.
Telekinetic Talents: Scarlet Witch
Scarlet Witch's psionic energy is capable of manipulating on a molecular level, leaving nothing safe from her potential influence. Wanda is one of the few beings capable of damaging vibranium, and her telekinesis even gives Vision and Thanos a run for their money. Her ability to move practically anything through space gives Wanda a greater potential in battle, with almost unlimited weaponry at her disposal.
Although Doctor Strange is quite capable of telekinesis, he does not seem to use it very often, except when obtaining precious artifacts from their former owners.
Intelligence Level: Doctor Strange
Even by a doctor's standard, Steven's intelligence level is impressively high, making him a modern-day Einstein (with an inflated ego to boot!). The Supreme Sorcerer can effectively retain vast quantities of information thanks to his photographic memory, making him the ideal candidate for absorbing the required information for spell casting.
Not to say that Scarlet Witch is dumb; it must take an acute level of emotional intelligence (aka EQ) to read people adequately enough to make her illusory hypnosis as effective as possible. There is no use instilling say, arachnophobic hallucinations on the Hulk, as he would likely just, well, smash the imaginary eight-legged assailants away.
Powers of Levitation: Scarlet Witch
As much as fans love the quirky personality of the Cloak of Levitation, the fact remains that Doctor Strange cannot defy gravity without it. In the instances where the Cloak is no longer in his possession, Steven either has to make a plan to retrieve his magical item or carry on without his levitating abilities.
Wanda's powers of flight, however, stem from the psionic energy that radiates from within her, resulting from a delicate balance between upward thrust and gravity. As her skills improve, Wanda is able to traverse greater distances and even lift other objects up with her, regardless of their mass.
Time Manipulation: Doctor Strange
There is no battle here, as the Master of Time is a title easily bestowed upon Doctor Strange. While Scarlet Witch is capable of altering the timeline, her powers are only effective within the Hex, and cannot be applied to the 'real world'.
Unfortunately, Steven has to rely on the Eye of Agamotto (in conjunction with the Time Stone) to effectively manipulate time, and he is essentially able to initiate change in any location throughout the universe. Doctor Strange's ability to see into the future is a saving grace in the fight against Thanos, although Steven sacrificed these particular skills when he handed over the Time Stone.
Healing Capabilities: Scarlet Witch
No, no, not medical skills, Dr. Steven Strange would have an unfair advantage on this front! In terms of magical healing, Wanda is able to assist in reconstructing Vision's body due to her ability to telekinetically revive him on a molecular level, and yes, she can perform this trick on humans too.
Receiving his powers seems to have altered the status of Steven's Hippocratic Oath, as he appears to not use his magic for treating the ill or wounded. This is not, however, a heartless decision, as all the Sorcerers agree that too much magical interference will disrupt the timeline significantly, with potentially disastrous results.
Defensive Maneuvers: Draw
Attacking head-on is not always the best option, as sometimes defensive options are better suited to distract or escape from the enemy. Both Wanda and Doctor Strange are able to create energy shields of some form, although Scarlet Witch's defenses appear to cover a larger surface area than her colleague's. Steven's evasive maneuvers are on point, as he can easily construct a portal when a hasty departure is in order. Steven can also alter the structural integrity of an attack, turning a deadly blast into a harmless kaleidoscope of butterflies, not to mention the Eldritch Whips' seemingly endless capabilities.
Scarlet Witch's mental manipulations are not to be underestimated, as her hallucinations can render her target immobile, lost within a battle in their own minds, and rendered virtually useless. Once under hypnosis, Wanda can also influence her targets' movements (as with the mass evacuation of Sokovia). Even the Mind Stone is not immune to the force of Scarlet Witch, and if an attack is imminent, Wanda can utilize her energy absorption to lessen the blow. She can also bequeath powers onto her allies, bulking up her teammates during a crisis.
The Battle Of Earth: Scarlet Witch
Not to say that Doctor Strange was useless during the Battle of Earth, but he was more of an observer than a combatant. With the vital task of reading all possible future outcomes, Steven didn't partake in very much action, and when he did eventually come face-to-face with Thanos, his Eldrich Magic was no match for the Gauntlet.
Scarlet Witch, on the other hand, managed to make Thanos sweat as she beat him down with a bombardment of grief-fueled attacks. After destroying his Double-Edged Sword, Wanda begins slowly ripping Thanos apart piece by piece, and, if the diabolical Sanctuary II did not intervene, Scarlet Witch would have likely walked off victorious in this standoff.
Flaws And Weaknesses: Scarlet Witch
The biggest downfall to Wanda's otherwise limitless supply of psionic powers is her focus and endurance. Some skills take a physical toll on her, whereas others require intense levels of concentration. If distracted or restricted, Wanda is about as useful as any other human. Her emotions also affect her powers, and Scarlet Witch has unintentionally hurt innocents in the past; however, her intense feelings have also been known to give Wanda a boost in strength, as with Vision's death.
As capable as Doctor Strange is of standing his own ground, he is unfortunately heavily reliant on the tools of his trade. Various OP artifacts are at his disposal, each with their own perks and purposes, however, objects can always be lost, stolen, or broken, leaving their owner suddenly without the additional support. Eldritch magic is also very dependent on spellcasting, which is a tricky and complicated process. True, what has been learned cannot be unlearned, but it can be forgotten, or the ritual could be performed incorrectly (and possibly at the most crucial moment).
Doctor Strange in the Multiverse of Madness is currently screening in theatres.