I thought Alfred Molina did a great job as Dr. Octopus. I'm not really a huge fan of Spider-Man 2, but I thought he really captured the character. And of course you have to mention Heath Ledger's Joker.
As for worst, I'm not saying this one is the worst, just want to add variation. I'm not pleased with how they did Two Face in The Dark Knight. The first half was great and the changes with how they made him Two Face worked, but he's a villain who deserves more than being an after thought in the Joker movie. And then killing him at the end in that way was lame.
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