This is a hard one because I love so many of them. Based solely on humor, A Christmas Story is as funny as it gets, and the only crying you'll do is the kind that comes from laughing too hard.
It's a Wonderful Life, A Christmas Carol (the Alastair Sim version), and Miracle on 34th Street (the one with Maureen O'Hara and Natalie Wood) round out the the top 4. I must see all of these at least once every year.
ETA how could I forget How the Grinch Stole Christmas!?!?!? This is right up there on my list of all time favorites. And not that god awful Jim Carey perversion of the classic with Boris Karloff.