We live in Florida, so your mileage may vary, but I LOVE St. Martin in September/October. Some restaurants are closed, certainly, but you won't go hungry. You also won't need a reservation, pretty much anywhere. No problems with traffic jams. The water is WARM, which is totally lovely to me. You probably will need a/c to sleep at night (but I personally always do). The prices for hotels, cars, airfare, etc., will be at their cheapest that they are for the entire year. What's not to love??