Oh Kid Buu yeah he's the real Buu and the wildest, the rather fat one is Evil Buu and there is one more a fat one who is really child like, because he has 7 different forms he was given nicknames, his name is Majin Buu but because there are so many people call him something different for each form.
The only ones I know are:
Good Buu (Mr. Buu)
Evil Buu
Majin Buu
Super Buu
Kid Buu
I think one is called Fusion Buu as well?