1. A Christmas Carol
2. The Doctor, the Widow, and the Wardrobe
3. The Next Doctor
4. The End of Time
5. Voyage of the Damned
6. The Christmas Invasion
7. The Runaway Bride
"The Next Doctor" would be ranked higher (possibly even first place) if wasn't for the horrible second half of the episode. After the terrific mystery behind Jackson Lake was solved, the story took a nosedive by shoving Jackson to the background (Jackson should have saved his son, not The Doctor!), degraded the wonderful Mrs. Hartigan to a one-dimensional, cackling villainous, and the less said about the giant cyberpunk Cyberking the better.
I don't really regard "The End of Time" as a Christmas special, but I ranked in the appropriate spot nonetheless. In a rare case, the second episode was actually much better than the first, but the overall production still had a lot of flaws. The last 15 minutes is pure brilliance. Also, Wilf is amazing.
Before "A Christmas Carol" came along, I hadn't been impressed by any of the Christmas specials (although, again, "The Next Doctor" came close). This is amplified by the fact "The Doctor, the Widow, and the Wardrobe," which was just a simple romp and not much more, is in second place. Alas.