The only Christmas movies I still watch as an adult are the various versions of A Christmas Carol. My favorite is the 1951 Alastair Sim one, but it's pretty hard to mess up. I'll watch ones with The Muppets, Captain Picard, and General Patton too.
I have a vast array of Christmas specials on my media drive, though. A Wish For Wings That Work, Will Vinton's Claymation Christmas Celebration, A Garfield Christmas, The Best Christmas Pageant Ever, He-Man and She-Ra Christmas Special, A Charlie Brown Christmas, Rambo Christmas, Ghostbuster Christmas, Mario Christmas, Pac-Man Christmas, Sonic Christmas, Pikachu Christmas, I'll watch all that shit.