It's a difficult decision for me. If only this was like, a poll whereas you could choose more than one. In that case, it would be Majin Buu, Androids 17 and 18.
The Ginyu Force got owned so easily in my opinion, Omega Shenron was cool, so I suppose I should list him as one of my favorites, too. Broly was meh, King Cold sucks. Especially since he didn't do anything for the 3-second duration other than just get owned by Trunks. But hey, that's me.
Garlic Jr was too queer, Frieza was cool but then started being all queer and stuff...
y'know what? I'd rather not just state my opinion on every one of these villans, it'd take a while anyway. D: