What Character do you wish Marvel never created...
Mine is Venom. I've never been a fan, and now with the constant identity swapping I see him as pretty much a vaguely Bizzaro-like Spider-Man knock-off and we have plenty of those. Moreover, most of the Spider-"men", many of them, spun off of Venom. Venom, to me is like everything that's wrong with 90s, is very uncreative, and really is only interesting due to Black suit Spidey, but really could've stayed a one-off character.
I'm also not partial to Cable as he's part of the whole continuity mess problem X-Men has.