Hmm, that's tough.
Haunted Mansion wins, though. It wonderfully illustrates the magic that is a Disney ride: interactive and creative queue, a great build up to the actual ride (part of the queue, but the staging area before loading is fantastic), the use of effects and sounds is superb, and it fosters discussion once the ride is over (did we jump to our death, or did the murdering wife behead us?!).