It depends on the level of your snorkeling experience. Both have clear water and excellent structure. Do you want to do a beach snorkel, a boat snorkel or ?. My suggestion would be to do both and then make a comparison for yourself.
If you haven't done Stingray City in Grand Cayman, then I would suggest this. The rays are great, but they also take you to the outside reefs where the snorkeling is excellent.