If you're big eaters, the
free dining will save you a nice amount (especially at the values or mods). If September is your choice because of free dining, be prepared to start booking your ADRs just about as soon as you get the reservation; some of the TS restaurants are difficult-to-impossible to book! Be prepared to have alternatives.
For us, the fall, winter, and spring are when we prefer to be in WDW. We're not big on Florida heat (nor on the love bugs), so faced with your choice, we would opt for December. Plus, you can't beat the gorgeous Xmas decorations at that time............WDW always is lovely, but at that time of year, it looks truly magical!
