This discussion is for the bestest villians ever. Got a favorite villian you think is best? Go for it. Just a series with the bets villians? That's cool too.
Just stick to villians and try to do more than, "OMG! [insert] is the best 4evr! They're so cool/hawt/sexy/aweshome!", 'kay?
I think Batman has the best villians. Most of them are usually evil because they've been driven insane. They also occasionally make you question whether Batman himself is insane.
The best of the best are Joker and Harley Quinn. They're funny, they have a theme, and Joker at least has been in every series of Batman ever.