Kmathi, if you do go to Sapphire Beach, be aware there are rocks when trying to enter the water. If you go towards the north end of the beach, it's easier entry. The snorkeling is ok if the wind isn't blowing. It can get quite choppy. One of the crew members on the Emerald Princess told me that they usually go to Pineapple Beach. I haven't been there, so cannot personally recommend it. We normally go to St. John, too. Trunk Bay is normally very tranquil, great self-guided snorkel trail about 50 yards off the beach, beautiful beach, good facilities. It does cost to go over, $6/pp on the ferry. You can catch the ferry from Havensight, but I know the Red Hook schedule is on time as they use that for public transportation. The cab fare to Trunk Bay was $4-$5/pp, and the entrance fee to the park was around $4/pp. Here
is a link for the ferry schedule, if you're interested. The cab fare to get to Red Hook is $18/pp. Coki is a very nice beach, so is Magan's Bay. Sapphire will be less crowded.