Seeing how this thread has fallen apart already, how about I put some statements down and you simply agree to disagree with what I put? I think the easiest way to put this is to explain one of the more complex characters of one of the least complex arcs: The Buu Arc. So I’ll start off with Majin Buu. (Will dub/Viz/fanboy terms. I’m typing this on campus so I’m not going to reference anything so bear with me. Viewers discretion advised. And for the hell of it, spoiler alert). God, this is a long read so.. hopefully this will shed light and end this thread..finally!
With that being said, Majin Buu!!!
Majin (Chibi) Buu is made and causes all sorts of terror. He fights the Kaioshin, killing two and absorbing one. Which one you might ask? The southern Kai, the strongest and “burly” Kai. Now, I’m going to say this and answer erik’s initial question: Buu got stronger after absorbing that Kaio (Now known as “Buff” Buu). Now, we see this new Buu battle the Kaioshin we first see (Prince) and he’s getting destroyed. It seems like Buu is going to deliver the final blow when the highest Kaio, Dai Kaio (?) saves him. He then unleashes a massive attack on Buu that cuts him into spam cubes. However! Buu covers himself over him and absorbs him becoming what we know as “Fat Buu”. That Buu is sealed for sometime until fanboys wanted more Goku

So we fast-forward to Gohan, the last Kaioshin (supposedly), Babidi and Dabura. Vegeta and Goku are both fighting at SSj2 which allows Buu to go to “Full Power” and he is released from his seal. Now it gets interesting… Buu is insulted by Dabura, a character that is said to be at Cell’s level (“Perfect”, but I won’t get into that). Dabura is swatted away which leaves Gohan in shock seeing how in all fairness, he was fairly even with Dabura. Now, Gohan and Kaioshin are easily beaten and Vegeta arrives. This is where I’ll point out Buu’s current strength and the confusion of his power increase and/or decrease.Buu got stronger after absorbing the southern Kaio. As for the other one he absorbed, I’m going to say first off that the Southern one might have been stronger than him, if not even. I feel, again IMO, he wasn’t necessarily weakened by the other Kai, but his “kind influence”, didn’t give him a need to fight the way he did before. Doesn’t make much sense written out but yeah.
I’m going to leave it with (Fat) Buu, at the moment, is at least stronger than Chibi Buu, mm ‘kay. Let’s see, Vegeta comes and self-destructs, which is a futile effort. Goku fights that same Buu later as SSj3 and IMHO, is stronger than him. I think Goku wanted to fight him because 1) He’s Goku and likes to fight. 2) Had to stall for Trunks. Okay, Goku teaches the boys fusion, Goku leaves. Now..! Majin Buu splits in two: His evil and good form. He expels all of his anger and it forms an evil Buu that is stronger than him. He tries to turn the Evil Buu to chocolate but he is the one that is turned into chocolate and this causes another transformation (which is odd because the other times Buu turned people into candy, they just died).
Anyway, Buu becomes “Super Buu” and is now Stronger then either “Evil” or “Good/Fat/Mr.” individually, but IMO he’s weaker than the “Buff” Buu. Let’s see, Buu fights Gotenks, makes short work of him, is caught off guard by a few attacks and later fights Gotenks at SSj3. At this point, SSj3 Gotenks has surpassed SSj3 Goku at the very least BY FAR (Yes, Goku isn’t the strongest get over it).
At this point, Gotenks is on level with Buu, if not stronger. But unfortunately, his time runs out due to negligence and SSj3 draining time. It seems all is lost until, a super-duper powered up Mystic Gohan appears (That’s right, Mystic. No quotations because that’s the best way to call him so there)! Mystic Gohan beats the crap out of Buu; he’s clearly stronger than SSj3 Gotenks (despite Trunks’ side comments). So at this point we know that Gohan is stronger than Gotenks, who is stronger than Goku, who is then stronger than Vegeta in their highest respective forms. Now, Buu absorbs Gotenks and Piccolo and is stronger than Gohan. Goku comes back to Earth and Gohan is later absorbed creating the strongest Majin Buu in the entire series. One more time, this is the Southern Kai, Dai Kaio, Mystic Gohan, Piccolo, Goten, and Trunks. Shut your mouth; it’s the strongest Buu.
So yeah, Vegeta arrives and Goku fuses to make, sigh, Vegetto the strongest character in the Z universe (you win, Rocketman). Even though Vegetto (perhaps SSj2), makes short work of Buu, Buu is still levels above the rest. As we know, Vegetto is absorbed on purpose and Goku and Vegeta split in two. They find the pods where their allies are held only to be confronted by a mini-“Super” Buu (At this point everyone has been detached except the “Fat” Buu). Now, Goku tells Vegeta that he should’ve kept the earring. Why? Because they couldn’t face a “Super” Buu, let alone a “Super” Buu inside of a “Super” Buu! It would never work! So Goku calls Buu’s bluff only to see that it is hopeless. Vegeta detaches the “Fat Buu” and this leads to the ultimate confusion.
Taking all of their friends out and leaving the “Fat” Buu, the saiyans leave Buu’s body. Now, I believe we “Fat” is made up of the Southern and Dai Kaio, by removing those two, we are left with the initial Majin Buu (Chibi). What we do see, however, is Buu slowly changing back. For some reason, we see the “Buff” form but technically, that shouldn’t be. Was that to make the transformation more dramatic? Hell, the anime made good work of that, believe me!
This is the first time Vegeta and Goku see Chibi Buu and their reaction was basically judging a book by its cover. Wrong. Buu destroys the planet and Goku only has time to save Hercule and Dende (and Bee). Buu follows them and the final battle for the fate of the universe (again) is underway! Goku wins a game of rock-paper-scissors against Vegeta and gets to fight Buu first, obviously denying the chance to use the portara which would’ve made short work of this Buu. Goku goes SSj3 and IMO is on Chibi Buu’s level.
However, Buu’s level of stamina and the fact that he can regenerate gives Buu a slight edge. Goku explains the whole power drainage with SSj3 and how it’s different in the afterlife. He says he can go “Full Power” (ugh, Movie 13 FTL) and defeat Buu. Vegeta tries to buy time as SSj2 and Buu easily outclasses him. I mean, come on! He was beaten by the “Fat” Buu earlier and Toriyama didn’t bring Goku back just for Vegeta to save the day..

He spits out the “Fat” Buu( ZOMG, no Mr.) and is ready to fight. He goes after Hercule and is stopped by Mr. Buu! The two Buu’s battle and Goku can’t get to full power. In short, Chibi Buu is stronger, Goku makes a spirit bomb, and Buu dies. I would add more, but I’ve typed way, way too much and I feel so nerdy right now.. I’ll add more later but for now, use this for the basis of your “debates”. And please don't be foolish enough to quote this whole thing.. @_@
-Rick