Dragon Ball: Emperor Pilaf. I know he's just a bumbling idiot but the interactions with him were always hilarious. I wanted to choose King Piccolo but I don't think I ever really liked him, and the Piccolo we know to love in DBZ was pretty much only evil in that one tournament. Still, Piccolo Junior would probably be a close second to Pilaf.
Dragon Ball Z: Fat Buu. When he's still evil or when he's starting to become good with Hercule Satan and the dog. (What's the dog's name, Bee? Buu Bee lmfao!) I didn't really enjoy the adult Buu that had no chin and always talked like his mouth was full of mashed potatoes... he reminded me of the roach guy from the first Men in Black movie and I kind of found it unpleasant until he absorbed some of the Saiyans and had a face. Same kind of goes for Cell's first two forms... they were unpleasant to me... and Frieza's forms, fuck I must be picky. And Kid Buu was kind of dumb too. But really, this question's hard because what are my options? Frieza, Cell and Buu? Vegeta actually would be a close second as my favorite DBZ villain.
Dragon Ball GT: Super 17. No fucking around. No hiding in people's bodies. No shadow dragon bullshit. Super 17 was just an unstoppable (okay not forever) mass of power that had to be taken down with brute force... or at least should have been. The thing I didn't like is that they only really were able to defeat him because of Android 18 going "QQ I'M YOUR SISTER STOP IT" to the manipulate the "Android 17 half." Dude... I think they could have beat him with brute force if they put their minds to it. I guess it's because they were saving the spirit bomb for the finale.