In my view, this is a questionable generalization - although I agree to the extent that when we ourselves go to the main island of Anguilla, we are not going for the snorkeling off beach there. I think Creole Rock and the outer reef south south east off Pinel (just two examples) are as good if not better than most of what you can find in and around Anguilla - as a side comment, I think Prickly Pear has declined significantly over the last ten years. Also, it very much depends on where in Anguilla or SXM and, for anyone simply coming for a day or two, it very much depends on sea and weather conditions - that is why I always am reluctant to make too specific a recommendation for someone who is going to be there just there for a day - such folks are best served by going with an outfit like Paul or Bob run, and they will react to the particular day. There also is the issue of what you consider good snorkeling - some people are very happy just to see some turtles or a lot of fish - others think it lousy snorkeling unless there is a healthy and colorful coral reef - the latter being the thing which may not exist in another 20 years.