Fall is my favorite time of year in Hawaii. There is less rain, the ocean is warmer for diving and less people traveling. However, you need to avoid any holidays, including schools on year round fall break. Concur with Dave that the rainy season starts in the fall, so if you are looking at November, it could be hit or miss.
Regarding TS to stay in: I have gotten my best deals when other people cancel. A lot of owners in Hilton, Marriott or other TSs will lock in a week one year in advance and just prior to the penalty window (usually 30 days in advance), they will call and cancel. If you have your name on a standby list with RCI, or if you check the net on the Hilton web page every night to see what opened up, you can get a nice place to stay. Which resort and Island depends on where you want to stay and what you like to do. My 2 cents is that Oahu is very busy with lots to do, Maui is more island style with a nice blend of country and things to do, and the big island of Hawaii is more country with lots to do. Kauai is the garden isle and if it is the first visit and only island, I would recommend doing something more exciting.
