There are many many options in the Caribbean. Frankly, you have to decide what is right for YOU. Is your main objective beaches? natural beauty? marine life? history? exotic shopping? What I like might bore you, and what you like might kill me.
A very good idea is to read over the ship's shore excursions for each port. Whether or not you decide to go with the ship's excursions, this is a starting point to get an idea of what is available at that port.
We have done Eastern, Western, Southern, hodge podge, canal, all sorts of Caribbean cruises and enjoyed them all. Check out our trip report and pictures at Cruising with the Halls
for some ideas.
And Zack ... I am NOT getting on any zip line!!