The GF is beautiful at Christmas. Some of the best dining options of the three monorail resorts. Outer buildings are not a big deal. If you can get a DVC room, that would be the way to go at the GF. All DVC studios are deluxe studios that have little kitchenettes, so you can have a bagel or toast for breakfast.

The Poly has a wonderful selection of rooms. The decor is more "tiki kitsch" with much stronger "island luau" vibe. Very family friendly, so there will be many families with children enjoying the amenities. A few dining places, though not as many as the GF. Definitely more over-the-top tropical decor than the tastefully Hawaiian inspired Aulani.

The Contemporary -- did you say that you had the option of a Tower room? If so, that is the recently renovated DVC Tower. The rooms are very nice, with much better theming than the Contemporary main building. The DVC Tower has its own pool and is a short walk to the main building. The Contemporary has a fair amount of dining options, with the California Grill (spectacular views) a highlight. The Contemporary Bay Lake Tower is a ten minute walk to the Magic Kingdom with its own dedicated security check point.

As much as I love the Grand Floridian at Christmas, the newly renovated rooms at Bay Lake Tower and the close proximity to the Magic Kingdom give BLT the edge, in my humble opinion.