Well, normally I'm a DLH girl. However, at Christmas time I don't think you can beat GCH. The lobby is amazing with its huge tree, carol-playing pianist, and Santa, of course! You're right in the midst of all the holiday stuff, close to the parks, and it's...well, magical!
As far as the room size, most GCH rooms are smaller than the DLH rooms, but not bad for a family of 4. There are some that are much roomier and have 2 Q + daybed, but you're not guaranteed you'll get one so you just have to hope your request is honored. Those rooms tend to be near the lobby/elevators and they're pretty popular. The smallest rooms, in my experience, are the bunk bed rooms. There is no wiggle room, esp. when the trundle is pulled out. Keep in mind, too, that the bunk beds are not standard size, but are actually shorter than normal.
I have stayed at DLH at Christmas time and had a wonderful, wonderful experience there as well. We had a DTD-view room in the Dreams tower, looking out on a huge Christmas tree! We could hear the music and watch people dancing and having fun. We could see the fireworks, too--we pulled our daybed over and sat in front of the open sliders and enjoyed the atmosphere. Now, of course, there are no more sliders to open so I don't know whether or not you could hear the music and I don't think it would be quite as cool, but the renovated rooms ARE really nice (stayed in one in Jan). So...my close runner-up to GCH during the holidays would be DLH with DTD view (Dreams Tower).
I've never stayed at PPH, so I can't say how it compares. One reason I haven't stayed there, though, is because the rate is usually only $10/night less than DLH at the times I go and I much prefer the grounds and atmosphere of the other 2 resort hotels. One of these days, though, I want to try PPH concierge, as I think it's a great bargain when the great ap/promo deals are offered.