Ooh, we've had many a villains discussion. But one more can't be all that bad.
I think that the best villains are the ones who really are metaphors (or perhaps even equivalents) of real life's villains. Not the type of people who are fantastic devil-like creatures or cackling moustache-twitching baddies, but the characters who enter the scene subtly, controlling or manipulating people without extreme physical or supernatural force, and ultimately truly ruining their victims' lives. They really are generally the best villains (or should that be worst?), as they really leave a deep emotional imprint on the viewer. They're the type of personages who help turn a great number of the Disney films from diverting fairy tales into fully blooded and emotionally engaging parables of life; seeing them perform their wicked deeds isn't simply a bit of a thrill to the story, it's truly heartbreaking to watch. Such villains would include Scar, Honest John and Gideon, Frollo, Cinderella's stepmother and pretty much all of Dumbo's circus.
Of course, some moustache-twitching villains and highly theatrical devils are just so plain spectacular and embodying of evil that they are frankly just wonderful. Maleficent, Cruella De Vil, Chernabog and Jafar are all good examples of this. And everyone loves a comic villain, like the Queen of Hearts and Captain Hook.
