My favorite is "I Wish It Could Be Christmas Everyday", because my dad liked it and we always played it while decorating the tree when I was little. It brings back nice, happy childhood memories.
Least favorite by a mile is "Stay Another Day", which is a simp anthem disguised as a Christmas song, and then "All I Want For Christmas Is You" which is excruciating. Actually, I might overrule that and say I hate "Santa Baby" more, because it's just a gold digger begging for gifts.
Amazing: Basically anything Clamavi De Profundis; it's really powerful stuff.
Three of my favorites from the above playlist: God Rest Ye Merry Gentlemen, We Three Kings, and Christmas Medley.
As to what I hate, most of the stuff they play in stores; it's usually sappy and just feels a little slimy, and I know it's driving the employees crazy too. Not pleasant, although occasionally you'll hear something awesome. But that's pretty rare.