Pretty much anyone except Blitz, Amumu, and Shen. Why should I ever ban them when I know the other team always will? And even if they don't, meh. It'd be nice to see them in a game every once in a while.
I'll generally ask my team if they have any requests but if it is left up to me I just choose those that annoy me. My personal favorites are Akali, Singed, and Elise. I just find them way too obnoxious to want to deal with.