That's a tough one. We're going with Polynesian GV in June, because it's my favorite and we've never been able to afford it since we got married, but we'll be back at WL Jan. 2003 b/c it's DH's favorite.
It would come down to two things for us - how many people in your party. That's another reason we went for Polynesian in June - we'll be taking my nephew so that makes 5 for this trip and4 for Jan. WL only holds 4/room.
The other reason would be cost. WL is usually much cheaper, thus more affordable.