Pirates of the Caribbean, Haunted Mansion and Splash Mountain more or less in that order. It is sad that Splash is going because with the lack of creativity Disney has now (the longer we get away from Walt's death the less the imagineers seem to think the way he did) it cannot possibly eclipse the charm that Splash had. So it is a shame and I suspect it is going to be routinely thought of as the best ride Disney ever got rid of.
I love Pirates and Haunted Mansion and Splash because of the attention to detail. Also, the first two were just thought up on their own with no movie to predate it. They are classic creativity. Splash is from a movie, but that's where it ends. There is nothing in the movie like what is on the ride. They did it well.
Tower of Terror comes to mind as well for the very same reasons. The theming, the atmosphere, the music and the anticipation are all great.
Other things like Small World, Carousel of Progress, Hall of Presidents, etc. are all masterpieces, I think. American Adventure everyone loves.