Avengers: Infinity War - Power Ranking Every Character
3. Doctor Strange
Though he was just earning his wizarding stripes in his first appearance, Doctor Strange has now been elevated - by circimstance and natural gifts - to being the protector of Earth against all manner of interdimensional threats. And even though his predecessor (and her initially most obvious replacement) are now out of the picture, it is not just a marriage of convenience between the good doctor and his position.
He is genuinely the Chosen One of sorcerors (or he wouldn't have been able to get to where he is so quickly), and showed in Thor: Ragnarok how far his powers have already progressed since his debut.
He also comes with the added assistance of an Infinity Stone (though perhaps not for too long), which allows him mastery over time (which is the most key power of all of the Infinity Stones as it means he can predetermine most outcomes as long as he's in control of the Eye). On top of that he has all of his other spells and has shown a willingness to dabble in slightly darker arts too, and he's rightly considered the natural successor to Tony Stark as the leader of The Avengers.