My nomination goes to one that I have never slept through (actually I've never had a nap in an attraction!) but my Mom certainly enjoys a good 20+ minute nap at least once every time we visit.
The American Adventure in EPCOT
She says it is dark, cool, and the seats are just too comfy! In fact she confessed that one of the times we were doing our own thing she went to "see" the show so she could grab a quick rest
