It would be one of either the Large Body, the Flantastic Seven, or the Darkling for me. The Darkling seems to be like what happens to a Keyblade wielder. The Flantastic Seven Heartless seems like a cool and fun kind of species with how their mini games are. The Large Body is a round brawler who seems to use its own round body in comical ways.

I was shocked to hear how he sounded in the Kingdom Hearts 2 directly after beating the last game. He sounded so awkward, I couldn't take him seriously.

I would like to be part of the Heartless. They're the ones with the most varied bodies. Also, they have nice designs such as the fun Flantastic Seven and the cool Darkling.