Clefable, definitely. I've been playing Pokémon for a very, very long time, and in all those years, I never even gave Clefable a second thought. Then I decided to train one in Y because I started liking Clefairy (which is a Pokémon I only started to like because of ... hilarious fannish reasons) and knew I couldn't really use an under-evolved Pokémon in battles against my friends. So I evolved the one I was training and started using it in battles ... and then became a teensy bit notorious for having a Clefable that just will not die. And then all of a sudden, Clefable rocketed up my favorites list.
'Course, probably some of the reason why Clefable's so useful is because of its new type, but on the other hand, I don't care because all that matters to me is that my Clefable can take punches to the face and proceed to continue pissing opponents off. AND IT LOOKS PRECIOUS WHEN DOING SO. 8D
Tl;dr, Clefable is a beast. An adorable, squishy, pink, frilly beast. And I love it for that.