We went this past December, 12-16 and thought the timing was absolutely perfect. The crowds were incredibly light. We either walked on most rides or waited 5 minutes. A few were 20 min max. Plus, it's all decorated for the holidays. Also, since it's before the Christmas rush, the prices and availablity for hotels and airfares were very reasonable. The week before this would be great too, but I'd avoid anytime after it. The day we left (weekend) the crowds were 10 times heavier.