Floridian here. October weather can be quite hot and humid, though not nearly as bad as August. It can also be pleasant. October is the end of hurricane season and there is a chance you would have to reschedule, more so at the beginning of October. Avoid the week of Thanksgiving, including the weekends on either end; also avoid the last two weeks of December unless you really like crowds, higher prices, and long lines for everything. You can catch the end of the Food and Wine festival if you go in October or early November at Epcot.
The parks are normally decorated for Christmas in the week or so after Thanksgiving. MK is sooner because of the parties. Disney does more for Christmas than Halloween. However, the Christmas entertainment at MK does not start until the parties end, in the week or two preceding Christmas, when it is insanely crowded. The Halloween party is far more fun than the Christmas one, and the entertainment and characters are actually exclusive, unlike with the Christmas party. Main Street is decorated with dozens of jack o lanterns, which is neat to see. So, it depends on how important weather is to you and what sounds like more fun.
