I have a general rule that works with only rare exception: if it was composed before 1850, and sung in a style appropriate to its original composition, I will like it. A very large FEH! on anything else.
I’m not picky about style or origin, as long as it’s acquired a patina of tradition. For European carols, I’m very fond of recordings made by The Alfred Deller Consort in the 1950s and 60s. Deller, a countertenor, possessed both an incredible voice and a passion for preserving early music.
The Boar’s Head Carol
The entire Play of Daniel, as performed by the New York Pro Musica
Ditto re. the Play of Herod
Adeste Fidelis (must-be-Latin!)
I Saw Three Ships
Lullay My Liking
Here We Come a-Wassailing (never, never, never “a-Caroling,” which is a Beastly Anachronism)
Children Go Where I Send Thee (especially by Odetta)
The Cherry Tree Carol (the only carol that lets Joseph be a human being - “And Joseph flew in anger, in anger flew he - ‘Let the father of the baby gather cherries for thee!’” Also ascribes in utero miracle to Jesus.)
Three Little Drummers, by the Beers family (sixties-era folksingers)
A quasi-exception: Britten’s A Ceremony of Carols, a modern composition heavily influenced by traditional caroling.
A few real exceptions: White Christmas ain’t bad, but I loathe-loathe-loathe Bing Crosby and haven’t found a voice that properly balances the melancholy (Ella Fitzgerald’s version is too upbeat). Have Yourself a Merry Little Christmas works with Garland, but not so well with Sintra or Fitzgerald. And there are always a few pop stars who manage genuinely interesting carol recordings, but usually I never hear their names!
Stuff That Makes Me Gag: Country-western carols; “easy listening” carols (they’re easy to listen to, provided you’re deaf); most pop singers’ carols; all opera singers’ carols (truly swatting fly with a sledgehammer); Jingle Bells; parodies of Jingle Bells; carols derived from Jingle Bells; carols featuring the playing of real jingle bells, The Boston Pops (loathesome pablum for 364 days of the year, poisonously saccharine on the 365th); Frosty the Snowman, Rudolph…oh dear, I’ll stop now.
But I’m not too much of a Grinch not to love Grinchly music. I even like the Whos’ carol.