We have never had really good snorkeling in St. Maarten except for one time we had some okay snorkeling at Dawn Beach. If the wind is from the wrong way, though, that beach is too rough for snorkeling.
In Antigua, we did Eli's Eco Tour and had some really nice snorkeling and a lot of other good fun. They come highly recommended on another cruise board. http://www.adventureantigua.com/
Mariner of the Seas 3/30/08
"Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did do. So throw off the bowlines. Sail away from the safe harbor. Catch the trade winds in your sails. Explore. Dream. Discover."