I don't think I hated any of them, really. If I had to pick some annoying ones though, Misty in RBY is definitely a pain. Starmie is an amazing Pokemon and having to fight it so early is just...terrible, especially since I'm a Charmander kid. lol
As far as GSC goes, I am actually going to go with Chuck. That DynamicPunch... @_@ Especially since I normally don't have many team members that are good against Fighting. It seems like I always have a bunch of Normal types at this point in the game (unevolved Eevee doesn't help) and then I have like...Typhlosion and that isn't gonna cut it against Poliwrath lmao. Just a pain in the butt, really. I've always had more trouble with him than Whitney.