Welcome to cruise-chat. Sorry no one responded sooner to your question. Trunk Bay is beautiful and the snorkel trail is pretty neat - but it can get very crowded with cruise ship excursions. If snorkeling is your number one priority in St. Thomas, Buck Island and Turtle Cove offer excellent snorkeling. If this is your first time in St. Thomas, you might want to consider snorkeling at the beach next to Coral World.