...Certainly not the X-men. I hate them. They have so many alternate timelines, side dimensions, cross universes, secondary subplots, that if you look at a family tree for them, it has wavy lines, dotted lines, solid lines, green lines, red lines, blue lines, dashes, x's, and many more things.
Well the title does say Character, so why is everyone centering around Heroes? My favorite Hero is Spiderman... :P I don't know about villians though, most of them aren't really masterminds like the Joker..
Hands down my favorite Marvel character would have to be Gambit. Love the idea and concept behind the character. Also probably the only reason why i'll go see the new Wolverine movie is because Gambit is in it.
A thread about Marvel characters in general would be fine in the Popular Media section. Please go there to either find or create one, and casually mention what your favorite character is in the general flow of conversation.