EPCOT!
When you can listen to the holiday traditions of the various countries (told by special holiday characters from each of the countries...don't miss La Bufama (sp?) in Italy...she was the BEST!), watch the Holiday Arch lights (synchronized with Christmas music), see a show with Mickey and the gang lighting the big tree, sit through the Candlelight processional show, see all the countries decorated for Christmas and have the special "Peace on Earth" finale at the end of Illuminations...there's nothing to compare.
Yes, MK is nice because Main Street is decorated, but I would pick Epcot ANY DAY!