Depend on what you enjoy. Seven mile bech is said to be one of the best. For a bit of adventure, you could do a trip to sting ray city with Capt Marvin or Native Way Watersports to feed the stingrays (perfectly safe) and go snorkeling. There are also jet ski tours, the turtle farm...
Lots of things to do. But for my $$, the snorkeling, stingray city or scuba diving is where to spend your day.
Have fun and welcome to Cruise Addicts.
Mike