Nerdiness! I feel so at home!
Between Vader an voldy, I don't know much about Voldy, but intuition tells me Vader would force-pull Voldy's wand out of his hand.
As for an all-out villian brawl, you have villains like Ganondorf who can only be hurt by weapons other villains can't wield, so the winner would have to be someone who can manipulate heros to kill said villains for them
While most people would point to Palpatine for the clone wars, Palpatine never really said or did anything that convinced me he was actually capable of pulling off what the plot said he did. He accomplished it by the grace of the plot fairy.
Sir Baldwin is much better, as he could manipulate both heros and villains with ease. He is also incredibly ruthless: sure, many villains don't care about their pawns, but Baldwin cared deeply for Richard and Thamuz, and sacrificed them without any hesitation anyway. Now THAT'S ruthlessness. But Baldwin needs an army backing him up: he's not that impressive one-on-one.
Mithos: now we're getting somewhere! Mithos manipulate hundreds, maybe even thousands of heros and heroines to die for a cause he made up. Lines like "That is mere logic people are not moved by logic" Show that he is a capable manipulator, as opposed to the plot just saying he is. And unlike Sir Baldwin, Mithos is capable of holding his own against multiple opponents. But Mithos is a little unstable, and While he may have been able to pull the wool over most people's eyes, Loyd, and myself, both saw right through him.
I would give the prize to everybody's favorite parentalistic dracocidal false goddess, Myra. While Myra may not like fighting, She's the best villain I've ever seen at manipulating heros. She could probably get the hero who defeated each of the villains we're discussing to kill them, and then get the townspeople to kill all of those heros for fear of their power. Myra wasn't just persuasive to the characters within the story, I almost feel for her facile view of what the world should be, because she actually made some pretty good points. When you can (almost) manipulate someone who is an outsider to the story, then you're a real manipulator. In addition, Myra can hold her own if attacked, assuming you can figure out where the **** she is, and that is a pretty big assumption.