Well no-one, but if I had to choose anything it would be something from the Tales series, and not a lead male. I feel they work better for 2D fighters though, and particularly Judith who would fit right in in Marvel, no? I'm sure Raven would work fairly well.
Errrr... honestly though, while I have liked every guest character style I've used bar Yoda, I would rather they focus on working their own characters into the game... Bangoo, Zasalamel reincarnation, Adult Talim, Older Yun-seung, etc. Those are far more important.