This one is a close second behind Martina McBride singing my favorite Oh Holy Night!

My religious choice is "It Came Upon a Midnight Clear" and secular "The Christmas Song".

I chose to have two as both serve a different purpose.

Mele Kalikimaka from National Lampoon's Christmas Vacation

I love this one.
https://www.youtube.com/watch?v=xzV9DIL_vrM

I have 2.
Merry Christmas Darling by the Carpenters &
Last Christmas by George Michael. I love the music & the beat.
https://www.youtube.com/watch?v=E8gmARGvPlI

Probably my 2nd favorite. The first being "O Holy Night."
Both by "The Ray Conniff Singers" on the best Christmas album ever.

https://www.youtube.com/watch?v=Jdl6O4cFlUs

It would be great to get a clean DVD of the full show of this:
https://www.youtube.com/watch?v=6UFBSzBdIt4

I Want a Hippopotamus for Christmas!

Hippopotamus? You can't be serious.

Cohen's "Hallelujah" sung by k.d.lang. Although I guess that's not really a Christmas song. So I would add "Mary Did You Know" sung by Pentatonix. Such amazing artists!

Christmas in Dixie Alabama

Grinch song sung by.....
 

... a man named Thurl Ravenscroft. His name was accidentely left out of the credits, which has led many people to think it is Mr. Karloff singing. He was also the voice of Tony the Tiger, and sang on many, many songs, including singing the bass part on the cast album of the film of "South Pacific". It's his voice you hear on the great bass part in "Nothing Like a Dame". He had a very prolific career as a singer and voice performer.

B.

Favorite Christmas Song
 

This is liking asking "What's your favorite Beatles song?" For me, impossible to answer. There are so many wonderful songs and great performances of those songs. Here's one you may have not heard but is a wonderful Christmas song. It's from a Disney Christmas Album from the early 80's.

B.

https://www.youtube.com/watch?v=-fk7Its9CGo

k.d.lang'.s rendition is absolutely wonderful

You are correct about not being a Christmas song. In fact most interpretations of this song are not religious. Cohen wrote about 80 verses to this song and refuses to disclose what he really is trying to convey. Extremely interesting song - google it sometime. Many people think this is a religious song because of the title Hallelujah but they really never listen to the words.