I like to go in Jan/Feb. I live in Ontario Canada. I love to getaway mid-winter, it makes winter easier to deal with. Anywhere is warmer than here in Jan/Feb.LOL
The crowd is smaller and the lines are shorter in winter. I just came back last week and oh man, I swear I will never go down there in summer ever again! It was so hot and so humit, so many people and all the lines are so long. All the good Fastpasses were gone by noon. The worst was that we were either baking in the sun or soak to the bone in t-storm, everyday, the whole trip.