Secret Harbor
This small, sandy beach is home to the Secret Harbor Resort. It is not a particularly large beach, and with all the resort stuff (chairs, hammocks, etc) spread out in the sand, it may feel a little on cramped side. But the water is very calm and perfect for swimming, so perhaps that won't be hard to get over.
The bottom is mostly sand, with some areas of rock that would warrant paying attention to where you're walking. The resort being onsite does have some benefits - there's a restaurant and bar that you should be able to take advantage of. It's also possible that you can use some resort equipment, like the floating raft or possibly some of the chairs.
Not the best beach for doing some snorkeling, but there is a rockier area on the right side of the beach that you should definitely check out if you're going to slap on the mask and snorkel.