It may depend on the exact weeks in question, but if I had no school schedule constraints, I'd pick early December. I have gone several Octobers and love it, but it does come with its own scheduling challenges (shortened days due to the Halloween party, jam-packed days to avoid Epcot during food and wine). It has also gotten to be quite a bit less empty during that time. I think that early December is still fairly slow, possibly more so that October. I'd like to see the Christmas decorations while the Christmas crowds and prices are not yet in full swing!