My favorite costume as a kid was the one I made myself - the headless horseman! Complete with a real jack-o-lantern. There wasn't much competition for favorite, because my parents dressed us up in humiliating costumes like crash- test dummies.
Our house is really secluded, so no trick-or-treaters. The one year that two little girls came by, my mother (who was not expecting anyone to visit) was in the middle of rinsing her mouth with peroxide - she was literally foaming at the mouth. They never came back.
I'd have to say Jack or Zero are my favorites, from TNBC. Now here's something to get your brain around: I recently discovered that Jack Skellington was voiced by Chris Sarandon, who played Prince Humperdink in The Princess Bride. He also did the voice of one of the baddies in Nausicaa. I couldn't believe it when I found that out!