As others have stated, with Stormalong Bay in the mix, it's a race for second place after that. We've stayed at just about every resort - here's our review:
Stormalong Bay - Yacht and Beach Club - 5 Stars - enough said already.
Old Man Island - Port Orleans Riverside - 4.5 Stars - Water falls from several features, a nice waterslide, all in a great themed setting. The one hot tub often gets a little crowded. Great pool bar in great setting as well.
Uzima - Animal Kingdom Lodget - 4.5 Stars - Huge pool painted to appear to have a natural bottom. Good waterslide. Hot tub set back in the foliage is great - especially at night. Step out of the pool and see the animals.
Nanea Volcano - Polynesian - 4.5 Stars - Smallish in size and often crowded are the only drawbacks. The Volcano slide is teriffic, going into complete darkness. No hot tub, but water jets and seating in the pool at the Great Ceremonial End. Hawaiian music plays underwater. Favorite pool bar with view of Cindy's Castle. Beach is steps away.
The Dig Site - Coronado Springs - 4 Stars - Great, long waterslide and very cool Mayan Steppe Pyramid are the highlights. One of the best playgrounds on property is adjacent.
Doubloon Lagoon - Port Orleans French Quarter - 4 Stars - Serpant slide (with Neptune (if you are true to the NO theme, King Triton if you stretch the truth a bit) is fun for the little swimmers, but short and very slow. The Aligator band and waterrfall add to the fun.
Beach Pool - Grand Floridian - 4 Stars - Great waterslide meandering through the rocks. Waterfall adds to the fun. Great Views from the pool.
Luna Park - Boardwalk - 4 Stars - The Keister Coaster is the centerpiece, but the amusement park atmosphere, the elephant, etc. add to the experience.
Silver Creek - Wilderness Lodge 4 Stars - Wonderful Setting, very serene. A shorter waterslide is the only drawback
Caribbean Pool at Old Port Royale - Caribbean Beach - 3.5 Stars - Smaller pool, very short but very quick water slide. Cool Fortress theming, which was better when the water guns actually worked.
Main Pool - Contemporary - 3.5 Stars - Long, meandering waterslide is very good. Waterfront view is also nice. Pool is plainish.
Community Pool - Old Key West - 3 Stars - very limited theming and no water slide (unless one recently opened)
Feature Pools - All Star Resorts - 3 Stars - no water slides, but some fun theming. Often very crowded.
We've not experienced the pools at Saratoga Springs nor Pop Century. Hope this helps somebody.