[Ashcan Bill]

On each cruise line's web site they list excursions specific to each cruise. Everything from snorkeling to horseback riding to zip lining to shopping tours to historical walking tours. Just depends on your interests.

You can usually book most of the same tours once you get in port for a little less money. The trade off is tour operator isn't vetted by the cruise line so the safety/reliability may or may not be the same. Also when you book a tour through the cruise line they absolutely guarantee the ship will wait for you if the excursion is late getting back. If you book on your own and for some reason are late getting back, you may find an empty spot where the ship was docked. Again, depends on how important saving some bucks are to you.

If you only plan to see a port once in your life, it's worth it (to me at least) to get out and see some of the city or surrounding countryside. If you just walk around the port areas by the ship, you'll get to see many Diamond International stores but you'll never really see a city/countryside you traveled a hell of a long way to visit.

Lastly if you go to St. Maarten, it's a split island. Half Dutch, half French. I'd recommend a tour that takes you to both sides just so you get to see a bit of the difference in cultures.