I would go to WDW because I've been there 3 times and it's closer. My first three attractions would be:
1. Space Mountain - last time I went to MK, Space Mountain was closed for renovations, so it would be awesome to experience the new Space Mountain! I love roller coasters, and this one is even more awesome because it's in the dark so you never know when you're gonna drop.
2. Aerosmith Rock'n Roller Coaster - I got to ride it last summer, and it was great! I'm a huge fan of the band, so the combination of Aerosmith and roller coasters is really quite the experience.
3. Hollywood Tower of Terror - All of the suspense and special effects leading up to the actual ride make it all worth it for me. I actually like the drops! XD