That is open to what you like. We love the week after Thanksgiving. The crowds are lighter. The weekends are heavier because that is when the locals come. There are folks who love Sep. After Labor day the crowds are light, it is still hot in Fl. Others like late Oct to mid Nov. The crowds are fairly light except weekends, the Food and Wine Festival is going on. Other like the spring. Others prefer the hot summer time even with the crowds.
During the light times of year, you can do more in less time, you also have less time to do them. An example is the 2 weeks after Thanksgiving, most of the time Spectromagic is only on Sat nights. You may or may not have Wishes everynight. The slower times of year they close attractions for rehab. They try to have everything open during the busier times of year. In early Dec either Blizzard Beach or Typhoon Lagoon is closed. Only one is open. It comes down to, when you can go, what you are willing to deal with and how flexable you are to seeing certain things.