Here's what you wanna do, and you can make it a special trip or you can just pop over one day when you are in Epcot, but visit both the Boardwalk and Beach Club.
Give your self some time to walk around the Boardwalk, take in the atmosphere, and then go into the lobby to see the decorations. Boardwalk has the best "traditional" Christmas decorations on property (red and green glass bulbs on Christmas trees and garland, that kind of thing) as well as an amusement park made entirely of CHOCOLATE. Way cool.
After you've enjoyed the Boardwalk take a stroll over to the Beach Club. It's a short (5 minute tops) walk. In the Beach Club lobby they have a carousel made entirely of GINGERBREAD and CHOCOLATE. This is very neat as well. While you are over at the Beach Club stop in at Beaches and Cream for one of the best burgers and sundaes on property in this old fashioned 50's style diner joint.
If you have time and you want to see more the Swan/Dolphin are a short stroll away as well.
If you happen to do this while coming from Epcot you will enjoy the stroll out the International Gateway, what with the various decorations and music piped around the area. If you have anyone in your party who likes boats you can hop one of the Friendship Launches and cruise your way over to the Boardwalk. Really, if you decide to grab a bite to eat at the Beach Club or perhaps a beer at the Big River Grill or ESPN Club yo could easily make a very fun three plus hour Holiday excursion out of the Boardwalk/Beach Club area.
IMHO the Poly and Contemporary are underwhelming in their Holiday decor, and I've never been to AKL during the Holidays (but maybe I'll have to check it out this year based on the recommendations.