What, I have to choose just one? I don't think so.
Silent Night. Aside from just being an all around great song, there are a couple of recorded versions of it out there that I love -- Stevie Nicks' version from 1986 and Mahalia Jackson's gospel version. I could listen to those a thousand times. And then there was the church service at my church following the Columbine High School shootings. We sang "Silent Night" even though it was the middle of April, and candles were lit for all the victims of the shooting, and all the other lights were turned out, and it was one of the most beautiful moments of humanity I've ever been a part of. It was a special song to me before that, but ever since, it means just the slightest bit more. It's like a light in the darkness when all hope is lost...
O Holy Night. This one I love just because I do. It's a hell of a song. It is gorgeous. Even country singers can't manage to screw it up. I used to play an instrumental version of it on the piano when I was in high school that was totally awesome.
Christmas (Baby Please Come Home). The U2 version, but also the original version with Darlene Love. I just love how U2 rocked this song out; it's perfect for their hard-driving sound, and Bono's vocals just soar. It was on the first volume of A Very Special Christmas, which I bought one early December on a lunch break from Youth In Government. I believe I bought it on cassette so I could listen to it right away on my Walkman, and I damn near wore the tape out listening to it over and over. It's not Christmas time for me until I hear this song.
Fairytale of New York. This is by the Pogues. Strictly speaking, it's not really a Christmas song, but it is a song about a particular Christmas, which in rock and roll terms, makes it a Christmas song. The thing that I love about it is how the lyrics contrast with the pure joyfulness of the music itself. And the lyrics are clever.
Hark! the Herald Angels Sing. This was my first favorite Christmas hymn. I think my Grandma McEwen loved it, so I loved it too. We had an album of Christmas music by the Mormon Tabernacle Choir and I think it was the first time I understood how amazing choral music could be.
O Come O Come Emmanuel. This one, when properly done, is lovely. It should be simple and quiet. It's a prayer. It's not a bombastic "Christ is born!" chorus. I've heard a rash of crap versions of it lately, though, with too much going on, and that annoys me. Why mess with perfection?
Silver Bells. We sang this in 1st grade for our Christmas concert, which we took on the road to a couple of malls in Salt Lake City. I just remember loving the words, all about Christmas time in the city, and imagined how I would grow up and live in the city someday, and it would presumably be Christmas all the time. My mom drove all the way down to Salt Lake to see us sing, and then I got to go home with her instead of on the bus with the other kids. I loved that day.
I'm a sucker for Christmas music, but I'm also fussy about it. It can't be just ANY old Christmas music. It has to be good.