Thise depends, which series/point in the series we are talking about. For this, I shall explain.
Dragonball Z: In the Buu Arc, when Gohan first attained Ultimate/Mystic, yes, he was stronger than Goku at SSJ 3. But only for a short while.
Dragonball Super: Yes he definitely is! No argument here whatsoever. If Gohan at Ultimate could fight on equal terms with SSJB/SSGSS Goku, then he could easily overpower SSJ3 Goku in Super.
So the answer is yes and no.
gohan because goku ssj3 was same in powerlevel of fat buu and super buu is twice stronger than fat buu and gohan was beating super buu like anything so gohan mystic is stronger than goku ssj3.
a lot of people think it is majuub but it is actually gohan because mystic gohan is far stronger than SSJ3 Goku and SSj3 Goku is stronger than kid buu and majuub is a recarnation of kid buu and majin buu so ultimate gohan takes the cake.
Ultimate gohan isn't as strong as a ssj4 the last guy who said that is a total FANBOY with no life.... that's all there is to it......ultimate gohan is as strong as a ssj3..in the buu saga ssj3 goku and ultimate gohan were tied and in the movie 13 ssj3 goku single handedly defeated hirudegarn while ultimate gohan could not hit or block any of his attacks and at the end of DBZ ssj3 goku became the strongest after that 10 year training to fight kid buus reincarnation...and he trained him for 5 years...it took goku 15 years after ssj3 to beocme a ssj4
Ultimate Gohan, since he is stronger than SSJ Gotenks & SSJ3 Goku No, kid buu because he's like 50 times stronger than gohan buu, and it only took gotenks buu to beat him.
ultimate gohan is just as powerful as goku ssj3 and evil buu was on par with good buu maybe a little higher and the fact that gohan kicked both their asses when they combined attributed to the fact that gohan is stronger. Gohan is the strongest unfused character in Dragon Ball Z. He is, however, stronger then Gotenks.
buu is 5,000,000,000 x stronger
manga: gohan anime: goku manga : Gohan > SSJ3 Gotenks > SSJ Gotenks > SSJ3 Goku anime : SSJ Goku > Gohan if you see the filler inside buu Goku say they strong as the real one but still if go by manga SSJ Gotenks is enough for SSJ3 Goku
Goku easily
Gohan is way stronger. he defeated cell when he was a child and goku couldn't as an adult. after losing to cell Goku even admits that Gohan is stronger than he is. it is not about who can turn into level 2 or 3 super saiyan it is about who is the strongest. that's what the ? asks. Who is stronger. in this category Gohan clearly wins.
SSJ3 Goku is much stronger
goku Edit: Actually, SSJ3 Gotenks is much stronger, considering his SSJ1 form is already said to rival or even surpass Goku's SSJ3. Super Buu is about equal to Gotenks at SSJ3. And Chou Gohan is even stronger than that.
they are about the same but goku is a tiny bit stronger but not by much