I voted for the Christmas party because the question was what would I choose. From the follow-up question about crowds, though, you may have a better time with DAH. I really enjoy the parties because there is so much to do that's not offered on a normal day in MK (special parade, special fireworks, shows, special snacks, special meet and greets...). It's more than enough to fill the time even without riding any attractions. But if all you really want are lower crowds? Do DAH, not the party. The party will disappoint you if your main concern is smaller lines for attractions.