I would do Christmas. It is truly an experience. The parks will be crowded, but everyone seems to be in a festive mood. By arriving the 21st, you will be able to experience the EPCOT Santa's. If you arrive after the 24th, Santa returns to the North Pole. So, you will be able to get the full experience out of our visit. There is snow on Main Street, Christmas shows, Christmas parade, etc. You will not get the MK snow, shows, parade prior to approximately December 16. If you want to see that part of Christmas at MK, you will have to get the tickets for Mickeys Christmas Party.