I've been relying heavily on Vince Guaraldi's music for the classic Charlie Brown Christmas Special - instantly recognizable by both young and old and not the easiest stuff to do so you don't hear it played live much if at all. I do almost everything Vince ever did for holiday music but "Christmastime is Here" is a fav. I've also been doing some swing arrangements of standards like "White Christmas" and "Sleigh Ride" and some deep jazz versions of "O Little Town of Bethlehem" and "Santa Claus Is Coming To Town". But to answer your question, the song that gets the biggest reaction is "I'll Be Home For Christmas".