My wife's undisputed favorite has got to be The Year Without A Santa Claus (the heat mizer/snow mizer one).
Our daughter isn't to the age of talking yet - but the way she laughs at Squidward - I'd guess that she would pick The Bikini Bottom Christmas Special.
As for me:
Animation-wise I like to watch The Grinch & Rudolph & Garfield every year.
Live-action-wise I like Santa & Pete (James Earl Jones rocks) & Home Alone (Daniel Stern made a new Christmas movie last year called "Battle Of The Bulbs") & Santa Claus The Movie (that scene where Cornelia puts out the plate of food in the snow for Joe has been burned into my brain for 25 years!)
Just has to be the Star Wars Christmas Special. I'd love to see that again hehe.
Seriously though, there's an old comedy here called Only Fools and Horses, and they used to show one or other of the specials that had been produced. I wouldn't mind seeing one of those again.
Animation-wise The Snowman was always a classic.
Hmm, I'll have to pick up a tv guide.
My wifeand I watched it's A wonderful Life for the first time in 8 years recently. We remember back in the time it was "24 hours" of It's a Wonderful Life before TBS changed it to A Christmas story. It was actually refreshing to watch after so long. Still a really good movie, it just got overdone at Christmas. I am betting in a few years A Christmas Story will be the same way.