if u ask me Gohan is the only "round" character in dbz.
U actually see him grow and learn, and his emations, what he feels etc.
Goku is a very "falt character" like , I know he turns ssj etc but that's not what I mean, he doesn't learn anything. I mean he's almost the same character at the end of the series then in the beginning.
Vegeta is a round character too if u ask me. U c what he feels, u actually get to understand him. Same with Piccolo.I miss that with Goku and Tien etc.
Krillin is a round character too if u ask me. He learns a lot, evolves along with Gohan.
Gohan is in every saga, (xcept the one witnh the tournament in heaven but that is a filler anyways) and u c him grow up. That's my vision of a main character