this is the best week in my opinion. The crowds are low. I have heard though that the Cubs will be there will special events going on so I don't know if that will add traffic or not. I know there is also a special DIS meet there that week.
You'll love the decorations and the Christmas feel!! I've gone this week 3 years in a row and love it. I'm hoping to go this year, but work may have to come first this year.