Which is your favourite Halloween theme monster and why? Is it because they are the scariest, have created the best literature and film, or have an interesting mythology?
My favourite are witches. What I love is that there is no 'standard' depiction of a witch. They could be green and warty or beautiful and enchanting. While fictional witches make good entertainment, there is a strong following of real practicing witches who follow Wicca or Paganism, and I think they are unique in this matter. You don't have practicing mummies or ghosts for example.
My favourite Halloween monster has always the vampire. I don't mean the sparkle-in-the-sunlight, new age vamps, but the scary, I-will-suck-your-blood-and-make-you-my-slave vampires. The classic vamp was always the best vamp!