It somewhat depends upon the ages of your kids.
If you have the younger set, MK is the place to go and you can fill an entire day and not "do it all". It's similar to DL only it's physically larger, with about the same number of attractions as DL (lots and lots the "same" and many that we don't have out west)
If you have teenagers the the Disney / MGM studios is probably the best choice - especially if they like rollercoasters and drops (Rock'n Rollercoaster and Tower of Terror) And there's Star Wars, The Indiana Jones stunt show, the Great Movie Ride, The Little Mermaid show, the Animation building (is it still there even though they closed down this animation unit?), the backlot movie ride, The Walt Disney Story and many more.
But now EPCOT has some pretty nice rides (Test Track, Mission Space, Body Wars, Maelstrom in Norway). You can also spend an entire day at EPCOT and not do it all (
Every
Person
Comes
Out Tired). And there are lots of attractions for the entire family. Besides the attractions already mentioned, other "not to be missed" attractions are: The American Adventure (or is it Journey), China and Canadas Circle Vision movies, Impesion's de France (movie), Cranium Command in the "health" pavilion. I enjoy the Spaceship Earth show and if there's enough time the Universe of Energy show (this one is a good 45 minutes to get through)
Animal Kingom would be a place you could go to and do it all, and many things several times. It opens earlier in the morning and closes earlier in the evening.
I like the suggestion of Blizzard Beach or Typhoon Lagoon. You can spend a fun, active day at either of these water parks.
If you spend the day at the water parks or AK, then you could spend the evening at Pleasure Island if that's your thing