If you can only do one, do Grand Floridian. It hurts my heart because frankly, against number 2, it's not quite as good... but it has the gingerbread house which is a must see, so that's the unique selling point.
My number two is Wilderness Lodge. There's frankly nothing special, decoration-wise, but the lobby features the token towering tree as well as the year-round fireplace and spots to sit. It really feels like you've stepped inside a Northwest ski lodge and it's as Christmas as it gets. Fort Wolderness is also great as the campers all decorate their campsite.
Honestly, all ththe Deluxes are great. You can probably skip Poly as it doesn't decorate much... the power rankings after GF and WL probably go:
- Beach Club
- Boardwalk
- Swan and Dolphin
- Contemporary
- Animal Kingdom Lodge
- Polynesian