Carol of the Bells is my all time traditional sound of Christmas. I also religiously (sic) watch the Festival of 9 carols every Christmas Eve. A household tradition.
Not religious either but do love the sound of a proper choir in a church/cathedral singing a carol, not such a fan of the modern twists like Pentatonix. That In Dulco Jubilo is perfect. I like Hark The Herald Angels Sing, The First Noel and O Come All Ye Faithful.
God Rest Ye and Hark the Herald Angels.
I'm not a religious man, and I'm past being invited to kids Christmas productions, so I hardly hear them. I might make a point of downloading a few. I think I still prefer them to all the 70s Christmas "classics" which I could quite happily never hear again.
Good King Wenceslas last looked out,
From his bedroom window.
Silly b***r he fell out,
Landing on a cinder.
Brightly shone his **** that night,
Though the frost was cruel.
So they used it as a light
Saving winter fuel.