So which one is that

Fat Buu

This is the form of Buu that we see first in the Buu Saga. Fat Buu is Pure Buu combined with South Kaioushin and Dai Kaioushin. He is the weakest of all of the Buus. Fat Buu later heals Mr. Satan's dog and talks to Mr. Satan. Mr. Satan tells Buu that killing is not fun, but wrong. Fat Buu then becomes friends with Mr. Satan and says that he will not kill again.

Good Buu

This is Fat Buu after he gets enraged with anger and splits into Good Buu and Evil Buu. This is just Dai Kaioushin and South Kaioushin in a Buu form. There is no more Evil Buu tied in with this form and he still has a great amount of power. He and Mr Satan are very good friends.

Evil Buu

This is the evil half of Fat Buu. All the evil in Fat Buu was exerted from his body due to his enraged anger when the people shot Mr. Satan and his dog. He's more powerful than Good Buu and fights somewhat without restraint.

Super Buu

This Buu is formed when evil Buu seperates from Fat Buu and then absorbs Fat Buu. He is evil because of evil Buu, but will not harm Mr. Satan or his dog because of Fat Buu. Since the more powerful and leaner Evil Buu is used as the base Super Buu's form is more fit for fighting. He also has a sweat tooth because of Fat Buu.

Super Gotenks Buu

This Buu is formed when Super Buu absorbs Gotenks and Piccolo. He is very intelligent and has an extreme amount of power.

Super Piccolo Buu

This form of Buu is when Gotenks fusion inside of Buu wears off (the fusion can only last 30 minutes). Because of this it has made Buu significantly weaker, but he still has his intelligence due to the absorption of Piccolo.

Super Gohan Buu

This form is the most powerful form of Buu. This form of Buu has abosorbed Gohan and has given him unbelievable power. This form of Buu has Gohan and every one abosorbed from Super Piccolo Buu on down to Fat Buu.

Majin Buu

This is the original and pure form of Majin Buu. This is the form in which no one is absorbed and he is exactly like he was when Bibidi first created him. He is now pure evil and fights with absolutely no restraint. He kills without remorse and likes to play and torment with his victims before he actually brings them to death.

Super Majin Buu

This form is Majin Buu after he has absorbed South Kaioushin. Now he is very huge and muscular and is still evil and extremely dangerous.

Uub

Super Uub

This is the merging of Uub and Good Buu. He is very powerful and now he is able to use some of Buu's techniques like "Become Chocolate".