...you ALWAYS get more bang for the buck by setting up your own dive outings. They are always less expensive than going with the ships outings. The only exception I have found to this was in St. Maartin, where the dive operation I chose was the same one the ship used. The cost was a wash.
If you go to the Rodales website (I think its scubadiving.com) you can do a search by location for dive operations and read about the different operators and what people thought of them. I use this a lot before going on a cruise. As far as I can remember, I have never been disappointed selecting dive operations this way.
As for hurricane season, make sure you buy the travel insurance so in case the cruise is cancled, you can get your money back...