Space Mountain is by far his favorite. I would love to take him to Epcot but I am concerned that the kids would be bored.
I like Space Mountain as well. I tend to spend one day in each park, with MK being two days. And, we go in October, when crowd levels are low. Neither my DW, dds, nor I have ever been bored at any of the parks. Plus, I enjoy restaurants, so we plan a TS once a day. Here are my highlights for each park.
MK has Space Mountain, Spash Mountain, and Big Thunder Mountain Railroad. They also have rides like themed rides like Jungle Cruise, Pirates of the Carribean, Dumbo, Pooh, etc. And, I like IASW there.
Epcot has Soarin (from DL), Test Track, and Mission Space as big three. We save Spaceship Earth (inside the ball) until the end of the day when the crowd levels are low. My dds and I love the Figment of the Imagination ride. The World Showcase has countries like Mexico and Norway that have a themed boatride inside. Others have short movies.
DHS has the Aerosmith Rockin Roller Coaster, Tower of Terror, Star Tours, Backlot Tours, and Toy Story Mania. It is difficult to get all those shows in one day. We will alternate between Indiana Jones, Lights Motor Action stunt car show, Voyage of Little Mermaid.
AKL has the Safari ride (my favorite), Expedition Everest, Dinosaur Ride simulator, and Primevil Whirl. I hope they still have Festival of the Lion King Show. Then there is the Nemo Show as well. AKL is usually only opened to 6:00 PM. It is the biggest park and is a lot of walking.
Have a great trip.