I've said it before, and I'll say it again! Santa Clause Is Coming to Town! I
Other than that, I like all of the other Santa Clause cartoons, Rudolf's Shiney Newyear, (shamefully unfamiliar with the first one), the original Frosty, and (not sure if this is the exact title), The First Christmas. It's the one about the Sheepherd that looses his sight.
know now of course that it was not the first one made, but it was the first one I ever saw, and so I will always think of it as the first one! The songs are great, and I just love the whole "bad guy turns good" idea in stories!