who would win in a fight?

Because I don't include GT in my DB arc, and Uub was holding his own against Goku, I'm gonna go with Uub.

If Adult Gohan is "Mystic" then Gohan, if not then most likely Uub but that's just me ~

I think Uub will win but once again he's freakin' overpowered , and no he shows up the first at the end of Dragon Ball Z after the Majin Buu arc soo he's a part of DBZ and eventually DBGT

always write that Gohan cause he is the best fighter for me

Firt of all id like to state that Gohan peak of power was at mystic gohan, which he got stronger than Buuhan, the strongest Buu in the series.

Uub , being the human reincarnation of KID BUU, has the potential to be as strong as KID BUU.

With that we would suppose Gohan > Uub, but, im not really sure of that cuz after all those years Gohan stopped training for good, and Uub traned hard with Goku, so, since Gohan would not get angry in a fight with a friend for no reason Uub got this.

BUT, if by any means Gohan gets really mad for some strong reason he´ll be stronger than anything, that was stated by Goku itself.

In normal conditions Uub will win.

At end of dbz saga Gohan would win as mystic gohan, since you said adult gohan i suppose you´re talking about the Gohan at the start of buu´s saga vs Uub first appearance.