What are your votes for the Best and Worst movie villains of all time? Let's see how deep into Pop-Culture the community can get!
Best

Character: The Emperor
Film: Return of the Jedi
I have never seen a character in a film that just OOZES evil like the Emperor in Return of the Jedi. Maybe that's because at the time I first saw it, I was too young to watch movies like Silence of the Lambs, but there's no other character that just personifies evil in the same way. Yeah, he looks like a weak old man literally wasting away before your eyes, but there's something in the voice, and the wicked charisma McDiarmid brought to the character. Every time I hear, "Now witness the firepower of this
fully armed and
operational battle station!" sends chills down my spine. As often as the Battle of Endor is derided, the land and space battles are just gravy. It's the cat-and-mouse mind games between Luke, Vader and the Emperor that is the true soul of the climax, and why the Luke and Vader duel in Return of the Jedi is, in my opinion, the best of all the duels and the highest point of the series. Empire Strikes Back may be the finest film in the series on the whole, but it's hard to deny that Lucas managed one last, truly great cinematic moment with this final confrontation.
And then, just when it seems the Emperor has failed, he reveals one last trick: He may look weak, but he nonetheless commands incredible power as he blasts Luke aside as if he were nothing. Vader may be the series's signature villain, but the fact that by the end of Return of the Jedi he becomes more accurately a tragic hero has to disqualify him for me. Proven in that the only way to finally stop the Emperor is his final act of sacrifice and redemption.
Worst

Character: The Emperor
Film: Revenge of the Sith
It's really sad how I had to do this. The one truly bright spot of the Prequel Trilogy was watching Palpatine make all of his puppets dance. McDiarmid was not exactly in full-on Emperor mode yet, but all the subtlety and charisma with which he portrayed the character in Return of the Jedi was in place. While the rest of the prequels lumbered around him, it was just FUN seeing him manipulate everyone around him to achieve his ends. They could have made all three movies JUST about Palpatine, and it would have been a FAR more enjoyable experience.
Unfortunately, he peaked at one line about half-way through Episode III: "I
am the Senate!" It was all down-hill from there. The most evil character in film suddenly became a platformer boss fight!
I mean it, seriously. The Emperor is sitting at the top of the Senate Chamber, while Yoda has to jump up the platforms to reach him while dodging other platforms being thrown at him. They turned the Emperor into Donkey Kong! Sure, there are a LOT of bad villains in film (Sean Connery in The Avengers, anyone?) but the fact that they took one of the BEST ever and made him into a cheesy video game boss is unforgivable.