I would say a lot depends on who you are traveling with and the tastes in your party.
Magic Kingdom: best for the younger kids and young at heart. That said, it is the quintessential Disney, and EVERYONE has to go at least once. We don't usually start here because a lot of the other parks pale after MK, and it is an exhausting park! We generally save it for the last park of our stay, and finish up with the fireworks and parade making for a very long last day, and very tired kids and adults on the flight home.
Animal Kingdom: our favorite too! Is that a Canadian thing? We often start with AK as our warm up park on a visit. It is a more relaxed pace, with not as many headliner attractions. You really can do it in a day. It also has more shade than the other parks, so it is easier to ease our pasty white Canadian hides into the Florida heat and sunshine there. Expedition Everest is still our kids favorite Disney ride.
Epcot: we can take it or leave it. It is big, spread out, and World Showcase is not overly interesting if you have kids. Still fun, but not top of our list. The whole park is a lot more educational, but also a lot more commercialized than the other parks.
DHS: Great for the older kids. ToT and Rockin' Roller Coaster are great rides for the thrill seeker set. Not as intense as some of the rides over at the Evil Kingdom (US/IOA), but still very good. Also more focus on the tween set shows from Disney (HSM etc). Enough good shows and attractions for adults too; not as much for the little tykes to do.