Oh wow hard question! I love Silent Night because I think it is just a beautiful song, I love We Three Kings too though but it is more because of the rhythm or cadence of the song and I love Santa Clause is Coming to Town because it is a fun song :D
I always loved "Merry Christmas, Neighbor". It was sung on the show Bonanza, by the Cartwright men. I found a cd last year of the whole show that had lots of songs and stories of Christmas. It's great! Look for it!!!