Epcot, no question about it. It's my daughter's, my wife's and my favorite park because there is so much to do and see that the whole family can enjoy, plus it feels less crowded than the other parks due to its layout and landscaping.
The Studios still feel like an incomplete park to me because it is very deficient in dark rides and too heavy on shows. Also, it's headlining attractions, the Tower of Terror and Rock n' Roller Coaster aren't very inviting to young kids, whereas Epcot's counterparts, Soarin' and Test Track, are much more accessible. The food at Epcot is also much better!