Shame you can't vote multiple times since Colossus, Cyclops, Shadowcat, Beast, Wolverine, and Emma Frost are all among my favourites of the actual X-Men teams as long as Joss Whedon's writing them. However, even though he wasn't a member of the X-Men (though he was and is currently on X-Factor), Jamie Madrox a.k.a. Multiple Man gets my vote. When Peer David is writing him (as he is now in the X-Factor series) he's the single most interesting character in comics as far as I'm concerned.