I haven't spent too much time up there, but
recall some worthwhile snorkeling at Creole Rock near Grand Case, St. Martin. Grand Case is home to numerous excellent restaurants, as well. Ile Fourche, between St. Maarten and St. Barth's had some decent snorkeling. There were only three boats there when we visited. There's a pretty beach on Tintamarre island, and it was totally deserted when were were there. If you can make your way down to
Saba, you'll find some great snorkeling and
diving.