We've stayed at the Divi Little Bay. Nice water for swimming, and you can swim off the beach to one of the areas where they take the snorkling party boats. Nice gentle bay to snorkle in, and some great fish / corals to see.
Easy to get to Phillipsburg, etc. Lots of boats / sailing in Phillipsburg. Of course, it's not hard to get to anything on the island. Dutch side is cheaper than the French side also - but if you want partially/unclotched scenary, you need to go to the french side for the best of that. The Divi beach does have some topless sunbathing though.