Disney World during Christmas is wonderful, but quite full. With that in mind, we avoid Magic Kingdom on Christmas day, as it is too full to enjoy, in our opinion.
Given the large number of people, I would not suggest a breakfast due to using up precious morning time when the parks are relatively empty. The one exception to that would be the last possible breakfast seating after an early morning in the park, which effectively turns it into a brunch. Even, then when we travel during high season we make our ADRs at restaurants that are quieter.
During low season I will happily eat at some of the noisy meals such as Chef Mickey or Biergarten, but during high season we try for quieter meals to help give us some down time.
In Epcot, I would suggest dinner at Bistro de Paris (the upstairs room in France).
If you really have to be in Magic Kingdom on Christmas, Cinderella's Royal Table is nice, but again rather expensive.
Believe it or not, one of our favorite places to have an ADR when things are hectic is the Plaza. It is a smaller restaurant and does not feel as frantic or get as loud as many places. The ample windows and light decor overlook some amazing people watching near the HUB. The food is not fancy, but we have always had a good meal there, and the ice cream treats are amazing.
I think there are great choices in resort dining. Jiko at AKL, California Grill, and Narcoossee's are all signature dining. Sanaa, Grand Floridian Cafe, and Boatwrights are all great options which are only one credit on the
DDP, if that is something you need to consider.
I had a blast a few years ago at Animal Kingdom. We got in early and did the headliners, picked up fast passes, and then did shows all day. The Jingle Jungle parade was wonderful. We had counter service at Flame Tree and were in line for them a couple of minutes before they opened, ate in the covered wooden structure overlooking EE and then headed over to Jiko for Dinner. It was a unique way to celebrate Christmas. It is still lovingly thought of as our African Christmas.
Have fun!