Best caribbean destination?

My husband and I are starting to think about next year's vacation. We would like to go sometime in May. It remains to be seen if we will be able to afford Hawaii, which is my first choice of destination. My second choice would be somewhere in the eastern or south eastern caribbean. My only concern about flying in and staying on a caribbean island would be running out of activities and things to do. I am sure we would spend some time laying on the beach...but you can only do that for so many days. I would also want to do alot of sightseeing and possibly be able to rent a self-guided boat (no guide) for a day to go explore on our own. Does anyone know of any islands that have a wide array of sightseeing and activities? I had Turks/Caicos and USVI at the top of my list. Would either of those be good? Thanks!