If you want to eat in a park, I would go with a restaurant in Epcot, for several reasons. There is a lot of holiday events going on in Epcot and they also have the largest number of really good restaurants--food wise, over the other parks.
If you want to eat at a resort, I would suggest either Artist Point in WL because the holiday atmosphere at WL is the best and they also have very good food. Or I would suggest one of the restaurants in the Epcot resorts. They also have very good food, there are holiday activites on the boardwalk--carolers, Santa, etc., and you will be just a walk away from all the holiday events at World Showcase.
The holiday season at WDW is very magical. We have been there for 3 Christmas' out of the past 6. This year we are staying home for Christmas but are going to WDW for New Years!
Have a great trip!