Xiahou Dun, definatly. Xiahou Yuan is cool, but... he has issues. Didn't it say somewhere that he really, really enjoyed killing people? Even in Ancient China, that's a little much I think, since I'd imagine most of the killing was done (unless you happen to be Dong Zhuo or any of his gang e.g. Li Jue, Guo Si, etc) because you had no choice, not because you enjoyed doing it. Yuan sounds like a sadist to me.
Plus, in the TV series he looked like an idiot at Mt. Ding Jun. Come to think of it, in the series he was very ratty-looking and weak. Didn't look threatening at all.
++ Wayne ++
"Better to wrong the world than let it wrong me!"
- Cao Cao