Hi Erin!
The Christmas season, in my opinion, is the best time to be at Disney. Disney really goes all out for Christmas, more so than any other holiday...
I am always impressed with the decorations at the Grand Floridian resort, if for no other reason, than the life-sized Gingerbread House they pull out during Christmas. The entire lobby area smells like ginger and cocoa...sigh...
They also have the rest of the lobby plus grounds area decorated pretty well for Christmas. Inside, there's an amazingly tall Christmas tree, and if you're lucky, you may catch a glimpse of Mickey dressed as Santa, as this is one of the resorts where he actually shows up to take pictures with Grand Floridian resort guests.
The Wilderness Lodge and the Contemporary are also high on my list in terms of decorations...
Hope you take lots of pictures and capture special memories!