F--- me; very close between No. 2 and No. 5, but I'll give the nod to five, since "Gimme Shelter" (always in contention for my favorite song ever, by any band).
EDIT: Huh. Not only have I never heard "Two Hangmen", I've never even heard OF it. So I went to YooToob, called up a video, and low and behold, the first comment was from Terry Talbot, the guy who wrote the song! That's cool! (Still never heard the song before, though).