It's impossible to choose!
I'd vote initially for Adventureland for POTC and JC, but Aladdin brings it down a few points.
I think theme-wise Frontierland and Liberty Square are the best, but skimpy on the ride department (though what rides they have are top 5 in the park).
Fantasyland is great but missing too many iconic rides for me to say its the top.
I still love Main Street but its a shell of its former self.
I'd have to say that Tomorrowland is my current least favorite but only because what's missing (Skyway, If you Had Wings, Mission to Mars, talking trashcan).