And just about anywhere you go on the WDW property, you'll feel it! I go the week after Thanksgiving so I can see the decorations, but not have to deal with the crowds associated with periods closer to the holiday season.
It's too bad you won't be able to see the Osborne Lights. They are... indescribable. If it's at all possible, they are one of the most beautiful things I've ever seen... and among the most tacky. It's wonderful and inspiring and silly and... well, truly unbelievable! I'm sorry they won't be up for my visit this year.
That said, all of the parks "dress" for the holidays, but, personally, I think Epcot might be the most festive of the parks. you get Santas from around the world, and many of the countries have shops featuring both trees decorated with native ornaments and beautiful decoratiosn to sell. Plus there's the beautiful Epcot tree, the carillion which usually plays at its base, and one of the most killer combos in any of the parks at the holiday season: The fountain dancing to holiday music as the international archway, decked out in multi-colored lights, flashes along in time. Stunning. I could watch this one for hours.
Also, if at all possible, buy tickets for the Very Merry Christmas Party held in the Magic Kingdom. Yes, it costs extra. But wow,is it worth it. They make it "snow" on Main Street, there are special performances and parades...it's a most magical time of the year! I'd say the Magic Kingdom might well be the second most festive park when it comes to decorating.
Take away the Osborne Lights festival, and nothing really jumps out at me as particularly outstanding decoration wise at MGM, but I might be forgetting. And that leaves Animal Kingdom the least well-decorated of the parks. Which is not to say it's not beautiful, just not... you know, packing that "wow" factor.
And yes, you can visit the resorts all you like. The Grand Floridian is particularly gorgeous at the Holiday season. If it's convenient for you to get to, I'd also recommend a visit to The Wilderness Lodge, which is SO gorgeous in and of itself, let alone when you throw in a rustic-Christmas kinda feel (and the humongous tree in the lobby!).
Have a great, great time!
Richard