Mr. Hankey The Christmas Poo (S1E9)
Merry Christmas, Charlie Manson! (S2E16)
Mr. Hankey’s Christmas Classics (S3E15)
A Very Crappy Christmas (S4E17)
Red Sleigh Down (S6E17)
It’s Christmas In Canada (S7E15)
Woodland Critter Christmas (S8E14)
Black Friday Trilogy (S17E7-9)
HappyHolograms (S18E10)
Bike Parade (S22E10)
Christmas Snow (S23E10)
South Park: Post COVID (S24E3-4)
I like most of them. Problem is that at least up to season 8, I’ve rewatched them so many times at Christmas that they aren’t as charming as the newer ones.
So choosing a gut-instinct favourite, I’d say Mr Hankey’s Christmas Classics, but I’d need to rewatch all to give a proper judgement.