OKW has a nice regular type pool--no big slide. You cannot use pools at any other resorts while staying at OKW unless you are a Disney Vacation Club member.
As far as best, many consider the pool at Beach/Yacht Club to be the best on site -- huge, sandy bottom, large slide and other things that make it like a mini warterpark. That one is so popular that they now meticulously check ID's to assure no one outside the resort is trying to sneak in; even DVC members can't use it unless staying there. The Boardwalk has a very good pool with the longest slide of any resort pools. Many others are also very good with slides, or little waterfalls or the like.