Horizons is number one for me.
The original Imagination ride is a close second. What is there now is not even close to the original. It’s like comparing the Snow White Scary Adventures to 7DMT.
I also miss World of Motion, although I don’t miss the long lines waiting to get in.
I also miss the skyride from Fantasyland to Tomorrowland. I saved a lot of wear and tear on my legs and feet using that to get from one side of MK to the other at a time when Main Street and Frontierland were the only stops on the train.
I miss If You Had Wings in MK. We rode it over and over during the days of ticket books because it was free.
I miss the animation tour at DHS, and the film with Walter Cronkite and Robin Williams.
There are some attractions I don’t miss so much, like 20,000 Leagues Under the Sea, and its fish dangling on string, or Body Wars shaking me to bits.