The 1948 version, of course. This is just such a wonderful movie, with outstanding performances (including especially Edmund Gwenn as Kris Kringle), the theme of "wonder vs. the scientific mindset" and a wonderfully "nice" twist ending, it's hard to find anything to disagree with it. Plus it has the iconic scene where the Post Office brings in bags and bags of mail "to Santa" into the courtroom; that's a scene that stands up against any other in cinema. "Christmas isn't just a day, it's a frame of mind."
This is one of those films that's worth it for the soundtrack alone. With all due respect to Jim Carrey, Boris Karloff will always be the Grinch to me. A wonderful tale that demonstrates that the spirit of the holiday is made up of genuine emotion and feeling for one's fellow people, rather than a particular religious event or commercial spend-fest.
There are a number of excellent interpretations of this story by Dickens (and more than a few awful ones), but I can't get enough of the George C. Scott version (1984). Mr. Magoo (1962) is a close second, though. I especially like it because it reminds us that in the Germanic mindset, Yuletide is the time when the veil between worlds is thinnest, and the shades of our ancestors walk the Earth (something that's reflected in the stories of the Wild Hunt, among many others). And the production values can't be beat.