The Gambit haters make me teh sad. (LOL! Not really.)
I don't like:
Cable
Jean
Cyclops
Sunspot
My reasons for Cable have already been stated by the OP. Cable is confusing.
I only tolerate Jean and Cyke in Evo, sometimes even like them a little, but everywhere else they're as bland as sugarless cake. They were a TINY bit more interesting in the movies, but not much.
Sunspot...long story there.
I used to actually hate him in Evo because I didn't want him to get together with Rahne because I 'ship Sam and Rahne like...insanely. Then I kinda got over hating him and now
just dislike him. He's too full of himself and stuff (Plus his codename sounds lame to me.
Sunspot? Ooh, scary.), but I have actually used him in stories since I now just dislike him.
Hmm...anyone else? Oh, there's Magik, but that's more of personal thing for me. Magik/magic itself shouldn't even be in the X-Men universe because it's more about science, IMO. She should've stayed dead. Same thing with Daytripper, but ironically I think her codename is cool sounding.
Sometimes I like Wolverine and even include him in stories, but overall am pretty tired of seeing the character everywhere. At least Hugh Jackman makes him seem cool and likeable.