Jedi: Yoda.
Sith: Emperor Palpatine.
I only watched the movies, though.
Watching the prequel trilogy, I was always confused whether Count Dooku actually was a bad guy.
Sure, he led the separatist movement and was a Sith, but wasn't he fighting Palpatine? And didn't he say several times that the Republic was under Sith influence, basically warning them?
Hmm, maybe I ought to watch those movies again to be sure...
I can't help the feeling that Dooku may only have been used to get the Jedi to trust the clone troopers (thereby allowing Palpatine to destroy them) and wasn't all that evil himself.