I can't say anything for WDW, but Disneyland my favorite smell is OBVIOUSLY Pirates of the Caribbean. I don't know what it's like at WDW but at Disneyland it's absolutely heavenly walking into that smell. I have no idea how to define the scent. It's something between "new car smell" and the musty smell you get in the mansion. Runner up would definitely be the vents at the candy palace.
@spacemt354 I'm FINALLY going to ride The Joker today. I'll be back with a trip report. I've been hearing amazing things about it. 14 moments of air time!