1. Magic Kingdom
Pluses: LOTS to do for all ages, it's the place you think about when you think about Disney World.
Minuses: Can't think of any
2. EPCOT
Pluses: Also lots to do, good variety
Minuses: World Showcase IMO - it's a long walk on a hot day, not a TON to see or do, also the fact that it doesn't open until later is a little inconvenient.
3. Animal Kingdom
Pluses: Has some of the more exciting rides, like EE and Dinosaur.
Minuses: Relatively few rides overall. To us, it was much more arduous of a walk, seemed like I was going uphill the whole time. The excavation playground is a bit of a cluster - hard to keep track of your kids unless you are right up on them.
4. DHS
Pluses: Shows, TSM, Rock-n-Roller coaster, ToT.
Negatives: Poorly laid out - always seems more crowded than the other parks. Crowds dampen the mood and there aren't enough restaurants IMHO - makes it a long wait to get lunch and difficult to find a seat.
Honestly, if DHS was laid out better, it would easily beat out AK.