Assume each person is in his or her prime. Each scientist can only use powers/abilities/weaponry associated with/discovered by/invented by him or her. The scientist’s known general demeanor should be considered — for instance, a feisty person would probably have the advantage over a sullen shut-in. No holds barred.
I’ll offer the match-up and you guys fight it out in the comments. I might update this post with a new duo if the discussion reaches a conclusive winner. I’ll start with some of my favorites. Ready?