Just picking one out of that list so I don't have to consider every IF we've ever seen, I'd say Coco. Being insane is fun. Being able to say just one word and have your closest friends understand you is awesome (my brother and I can actually do this). Being able to produce just about anything (nevermind where it comes from!) is just a bonus.
(And I've moved this to the appropriate category. Discussions that aren't about *specific* characters go in general Characters. It's not a huge deal but I try to keep the place consistent.)