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.