Both classics, but christmas story is from the perspective of a kid so I have to go with that, Then as you get older you can more and more relate to the parents and see the movie through a completely different perspective.
Of the two above I would pick 'A Christmas Story'.
Gremlins is great, never gets old.
I grew up on Christmas Story and it's always been on (24 hour marathon) at my family's but I swear I can't stand it anymore. I feel like I just watched it yesterday, even when a year has passed, it's not a good thing.
Christmas Vacation def wins my vote, good to remember Chevy when he was still funny.