Both are beautiful and a great choice.
Yacht Club has an understated elegance. The lobby has leather chairs, brass accents, mahagony, and other "higher end" fixtures.
Beach Club is very beachy--with wicker furniture and birdcages and "crafty" knicknacks.
Also, Yacht Club rooms all have full balconies, whereas Beach Club rooms have half balconies, and some look like they are too small to even use, and still other rooms do not even look like they offer balconies (not sure on that latter part).
We prefer Yacht Club b/c it is more elegant, but doesn't throw its elegance down your throat like Grand Floridian. Beach Club needed something else, we thought....
My vote is for Yacht Club.