At http://research.yale.edu/lawmeme/modules.php?name=News&file=article&sid=681 is a light discussion of copyright issues related to Christmas songs, with links to a poll in which you can vote for your favorite from a list of 12 songs. Greenfleeves and Filent Night are both on the list, though many other favorites aren't.

Silent Night currently has a slim lead over "Carol of the Bells".