Since you’re a coaster freak, at MK, Space Mountain would be a great choice for you…but who else will be going with you? If you have young children, any of the FantasyLand rides already mentioned would be a good bet.
Since you mentioned other parks, I think that at Epcot, Soarin’ is the ride to go on first if you can. If not, definately make its fastpass kiosk your first stop when you get to the park. Others you’d enjoy would probably be Mission Space and Test Track. If you have children, depending on their ages, Mission Space may not be the best choice for them though.
At MGM, if you need to feed your coaster fix, make Rock N Roller Coaster your first stop. For the kids, don’t forget Playhouse Disney or Voyage of the Little Mermaid (both live shows) if they’re younger. Teens would love RNRC and Tower of Terror.
At Animal Kingdom, since Expedition Everest won’t be open yet, try Dinosaur! for thrills , but your first ride should definately be Kilamanjaro Safaris.
Other than that, there are so many attractions that you’ll love…can hardly wait to read your first trip report! Have a great trip