If you mean a superhero: I suspect a lot of people will hate this idea, but... a Green Arrow game, set in the angsty Arrowverse world of the recent TV series, with all the supporting characters voicing their roles.
My biggest reason for picking this is I like playing characters who aren't nigh-invincible (like Superman, Wolverine or Deadpool) but for story purposes might as well be. And Batman's been done to death. And nobody seems keen to give the PC world a decent Spider-Man game.
On the other hand, if you literally just mean a Marvel or DC character: Phil Coulson, in a SHIELD game. Though that would have probably been best as a TellTale game, which I know nobody wants.
And this totally ignores the constraints of the question, but I'd like an X-Men action RPG (maybe by Bethesda or Obsidian) where you play as a no-name mutant you create, a la Freedom Force, who interacts with Professor X and the other regulars, to defeat Magneto or someone else.