We stayed at the YC for our Ann. last July and we were treated better then at any other resort we have stayed at.
It is a beautiful resort and surprisingly relaxing even though you are in the middle of the fun.
I have not stayed at any of them but I have visted all of them, and also seen the Yacht Club and Beach Club featured on Great Hotels. I do not like the decor of the Beach Club rooms, but thought the Yacht Club rooms were very pretty. I would choose Yacht Club of the three.
Beach Club.... but only because it's the only one I haven't stayed at yet.... YC and BW are also terrific resorts. You really can't go wrong with any of these choices.
If you want the awesome pool, then by all means, choose the Yacht or Beach Club. If you want it just for the great location by MGM and Epcot, I would totally go for the Swan or Dolphin with the cheap rates. Why pay double if you are never even in your room?