Vegeta for sure, it's a shame ol' Geets always gets done dirty though. Especially in Super, every time he gets a great moment it's followed instantly by him getting his shit kicked. That pummeling he gave Black needed more time to breath :(
Piccolo and pre-Buu saga Gohan are tied for second though. Piccolo developing from the most terrifying villain to the best father figure in the show was great to see and Hellzone Grenade is one of my all time favourite attacks in the show. Gohan's build up to SS2 was also just some of the best parts of the show.
Specifically for
Super though I really liked Hit, even though his introduction fight kinda sucked. Super in general falls into a hole of "the person I'm fighting randomly got more powerful because reasons" which DBZ never really did and it is a lot weaker for it, Hit is one of the most egregious examples of this in his first fight with Goku. His second fight is a lot better though and I like him a lot as a character.
I also liked Jiren. He's barely a character but I think it's just because he
doesn't fall into Super's "the person I'm fighting randomly got more powerful because reasons" hole. Jiren is OP
from the start. Rather than his power-ups feeling bullshit, anyone even landing a blow on him feels a bit bullshit. He's a walking wall for the characters and honestly I loved that he didn't have a gimmick, I remember as Super was airing talking in the OT on here and lots of us assumed Jiren would have some kind of gimmick as to why he was so strong and that would be his downfall but
no, he's just fucking STRONG.
Fuck GT tho.