My favorite beaches are: Trunk Bay, Grand Anse Beach, and Seven Mile Beach, in that order. The best snorkeling is: Xel-ha, Champagne Reef, Flamingo Bay, and Isla Catalina in that order. Trunk Bay is on St. John, Grand Anse is on Grenada, Seven Mile is on Grand Cayman. Xel-ha is on the mainland from Cozumel or any of the ports around there, Champagne Reef is in Dominica, Flamingo Bay is in Grenada, and Isla Catalina is in the Dominican Republic. This is just my list and I certainly haven't been to every island. Bonaire has some great snorkeling and Aruba has some really nice beaches as well. My preference is the southern Caribbean, but I'll take any of them