Hi,
France has published the 34th and last book of the Perfect Edition, with the "perfect translation". I read the hole Buu saga in that awesome edition, and it gave me the will to think again about power scaling, which is not clear in this saga. The best way to estimate them is, IMO, to be concentrated on Buu's forms and mechanism. With that, I think there are three possibilities that gave us pretty easilly a range for all "first" characters :
1) You think that only Dai Kaioshin weakened Pure Buu, and also that the monster absorbed South Dai Kaioshin because he was stronger than him :
- Pure Majin Buu : 40,000,000,000 (because he's the beginning on what all my operations will be focused, I gave him an arbitrary power of 40,000,000,000).
- South Kaioshin : 50,000,000,000
- Buu + South Kaioshin absorbed : 90,000,000,000
We know that this form of Buu is stronger than Super Buu.
- Super Buu : 70,000,000,000
- Majin Buu : 30,000,000,000 (Inferior to Pure Majin Buu)
- Pure Evil Buu :
18,000,000,000 if you think that his power is the majority of Majin Buu.
45,000,000,000 if you think that his power is the majority of Super Buu.
- Innocent Majin Buu :
12,000,000,000 if you think that his power is the majority of Majin Buu.
25,000,000,000 if you think that his power is the majority of Super Buu.
WIth that, we can also estimate power of heroes :
- Goku SSJ3 : 40,000,000,000
- Gohan : 100,000,000,000
- Gotenks SSJ3 : 75,000,000,000
So we can assume that :
Gohan is at best 2.5 stronger than Goku.
Super Buu is at best 1.8 stronger than Pure Majin Buu and Goku.
Gotenks is at best aroung 2 times stronger than Goku.
2) You think that only Dai Kaioshin weakened Pure Buu, but that the monster absorbed South Dai Kaioshin because he was putting a goood fight :
- Pure Majin Buu : 40,000,000,000
- South Kaioshin : 30,000,000,000
- Buu + South Kaioshin absorbed : 70,000,000,000
We know that this form of Buu is stronger than Super Buu.
- Super Buu : 55,000,000,000
- Majin Buu : 30,000,000,000
- Pure Evil Buu :
18,000,000,000 if you think that his power is the majority of Majin Buu.
35,000,000,000 if you think that his power is the majority of Super Buu.
- Innocent Majin Buu :
12,000,000,000 if you think that his power is the majority of Majin Buu.
20,000,000,000 if you think that his power is the majority of Super Buu.
WIth that, we can also estimate power of heroes :
- Goku SSJ3 : 40,000,000,000
- Gohan : 80,000,000,000
- Gotenks SSJ3 : 60,000,000,000
So we can assume that :
Gohan is at best 2 times stronger than Goku.
Super Buu is at best 1.4 stronger than Pure Majin Buu and Goku.
Gotenks is at best aroung 1.5 times stronger than Goku.
3) You think that all Kaioshin weakened Pure Buu :
- Pure Majin Buu : 40,000,000,000
- Buu + South Kaioshin absorbed : 35,000,000,000
We know that this form of Buu is stronger than Super Buu.
- Super Buu : 30,000,000,000
- Majin Buu : 20,000,000,000
- Pure Evil Buu :
12,000,000,000 if you think that his power is the majority of Majin Buu.
18,000,000,000 if you think that his power is the majority of Super Buu.
- Innocent Majin Buu :
8,000,000,000 if you think that his power is the majority of Majin Buu.
12,000,000,000 if you think that his power is the majority of Super Buu.
WIth that, we can also estimate power of heroes :
- Goku SSJ3 : 40,000,000,000
- Gohan : 50,000,000,000
- Gotenks SSJ3 : 35,000,000,000
So we can assume that :
[/list]Gohan is at best 1.3 times stronger than Goku.
Goku is at best 1.4 stronger than Super Buu.
Gotenks is around Goku's level.
My aim was to gather all "big" point of views on this debating saga and to delimate the range of power difference between characters. Hope you'll find it interesting ! 
