Goku Forum

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Well I'll throw my two cents in:  
 
Base form GT Goku is likely = to Buu Saga ssj3 Goku. 
Why? Because he has trained and was on par with a fully trained Uub, who is the reincarnation of Kid Buu. 
Base form Goku also shattered a dimension, somewhat comparable to Super Buu and Gotenks' ROSAT feat. 
GT Goku pre-ssj4 beat Rildo, who had a greater ki than Majin Buu.  
Also base form kid goku who was injured and had no energy left kicked away an Earth destroying attack by Yi Xing Long. 
Now ssj1 is 50 times base form, ssj2 is 100x base, ssj3 is 400x base, (all in Daizenshuu 7) 
There is no official multiplier for ssj4, but we know it is obviously bigger than 400x base.  Every ssj multiplier is at least double the previous one, so ssj4 would be 800x base form minimum. 
Also remember that turning into a child did not diminish Goku's power level, it only obstructed the Shunkan Ido technique and made ssj3 more draining.   
And the ssj4 transformation was so powerful that it undid the magic of Red Shen Long's granted wish made with the black star balls, and the black star DB's are said to grant any wish with no power restrictions. 
 
This being said I would conclude that ssj4 Goku is at least 800 times stronger than Buu saga ssj3 Goku, or (400 x 800) 320,000 times more powerful than base form Buu saga Goku.  
 
Now in terms of destructive power, GT is a direct sequel to the Z anime, and in the Z anime Kid Buu was depicted as destroying galaxies (also backed up by manga statements) and I have shown how much stronger ssj4 Goku would be then him.  
 
So long story short, he is much much more powerful than superman, lol.

@hitsusatsu11:  thanks man

@rein: I think he means ssj1 Gogeta or ssj4 Goku 
 

 
now i have something to ask, my brother said he thinks SSJGogeta is stronger then SS4 goku and i want to know what you guys think.

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Hard to say. 
First off, Gogeta is a product of Metomoreese fusion, now we don't know the specs on this fusion, but if it is like Potara fusion then it multiplies the fusers power together. (in daizenshuu)
So it stands to reason that Movie 12 Rebirth of Fusion Gogeta has the powerlevel of base form buu saga times the powerlevel of base form vegeta, as they were not ssj at the time. 
Its impossible to number guess the stronger between the 2, as we don't know there powerlevels. What I would base it on is that Goku told Goten that trying fusion as Gotenks wouldn't help in the fight and that ssj4 is the best bet.  
 
However if I go based on some rough estimated powerlevels: 
 
Goku ssj vs Freeza= 150,000,000 (Last official powerlevel) 
Goku post ROSAT vs Cell= what maybe 100 times stronger, so 15,000,000,000 (Remember from the 21st Budokai-ssj against Freeza we know he became 1 million x stronger in power level)  
Goku ssj Buu saga= maybe 10 times stronger, so  150,000,000,000. 
Now divide by 50 for Buu saga base (150,000,000,000/50) 300,000,000 
So Gogeta maybe could have a plv of (300,000,000 x 300,000,000) 90 000 000 000 000 000 base form, x 50 for ssj1,100 for ssj2, and 400 for ssj3 if he could.
 
Contrast with SSJ4 Goku who, if he is 800 times ssj3 Buu saga goku as I think, would be (300,000,000 x 400 x 800) 96,000,000,000,000  
 
However those assumptions I made could be wrong. Goku for instance says the strongest saiyan power he ever felt was Bebi Vegeta, and he said Rildo surpassed Buu (idk if he meant mystic) 
 
If im close to right on the plv of ssj4 though, it would make ssj4 gogeta at 9 216 000 000 000 000 000 000 000 000

If you think about it SSJ4 is really SSJ1

Also if you run by those calcs I made, and then scale for power based only on a) Goku running the 100 m in 8.5 seconds with a plv. of 10, and b) Roshi destroying the moon with a plv. of 139,(ignoring all statements and other things) then assume a linear relationship between plv and speed, and plv. and destructive capability, that ssj4 Gogeta plv. is capable of quadrillions of times lightspeed running, and can destroy quitillion's of sun's.

@rein: Based on the snake way speed calcs I have done, it is likely power level has more of an exponential relationship to abilities (speed in this case) then linear. This is also confirmed by the fact that say Piccolo Daimao with a plv of 260 can easily beat Roshi, plv. 139, Ten, plv. 180ish, Yamucha plv. idk shitty, all at the same time, even though the sum of their plv's are greater than his, even combined they cannot equal his capabilities. Its likely more then linear, but I just calc it with linear relationship to be on the safe side, that and I'm not about to bust out LOG paper and plot complex plv-ability graphs.

I think that SSJ4 is his power in SSJ3 as an adult because he have turn into a kid that probably cut his power in half.

@Destinyheroknight: Goku says his powerlevel did not drop at all as a child, he just could not IT or stay in ssj3 long because it drained his child body. 

@rein: He just said his power remained the same, but ssj3 put to much of a strain on his child body so he couldn't maintain it, he also can't use IT for some reason. Then in ssj4 the power is to great and it overrides the black star DB's wish and turns him into an adult for the duration of the transformation. 

@hitsusatsu11:
Sorry I don't believe that Goku is strong in his kid body. All the villains on GT don't seem as strong as kid buu. 

@Destinyheroknight: Ok, no need to apologize, I'm just saying what Goku said in the show.

@hitsusatsu11: 
I saying that Goku probably didn't notice his powers have change.  
Did anybody else on GT say that Goku strength was the same?

@Destinyheroknight: I can't remember off hand, the first half of GT kinda really sucked, and the rest was only moderately better so I don't often re watch it.  
Basically in his kid form he just can't maintain his energy, they pull out his tail and this helps, but he can't maintain energy as well as in adult form.

@hitsusatsu11: 
Gotenks can maintain his energy more then Goku kid form. Also Goku adapt to things pretty fast why he didn't do this time?