For me, in a good book the villain isn’t really evil or bad so much as misguided. A person who for some reason is making some bad choices. It’s a hard lesson to teach my students, but that’s the way it is in real life, too. No one actually thinks they’re the villain, even when they’re doing some pretty heinous stuff. We all have our own rationalizations and justifications. Which isn’t to say that morally some things are wrong, but I think it’s very rare that people don’t have some kind of justification for themselves when they do something others might consider wrong.
So, I like my villains sophisticated, and therefore, ambiguously villainish. I’ve had extensive debates with folks about whether Severus Snape from Harry Potter is a villain. I think that in the end, he’s not, though he does some fairly villainish things. I like Snape because he’s more complicated than Voldemort, and he demonstrates my theory of what makes a good villain…someone who has complex reasons for his actions but in the end is always redeemable. Think Darth Vader. Also, I want there to be some Slytherins who are not all bad, because the first time I ever got “sorted” (on my friend’s pda, I think), I came out Slytherin and have since developed a strong loyalty to my house.
Second place would be Eric from the Sookie Stackhouse mysteries. Again, is he a villain? I don’t know. But I recently read the mystery where Eric loses his memory and becomes all sweet and kittenish. Powerful, villainish man made helpless…yum.