This was our second time in San Juan and it was great. Part of our group walked to the main fort and others walked through town. All of us had a great time though and the park that is by the pier is very nice. We went back to the park after dinner and sat and chatted in some of the interesting yet comfy outdoor furniture that they have there. From the park you get a great view of the ships at night.
St. Thomas was beautiful! It was not a terribly long walk from the pier to the taxi stand. Once at the taxi stand, we went by taxi to Magen's Bay. Due to the size of our group (7 people for the trip to the beach) it cost us just $9 each way to and from Magen's Bay. It costs another $4 admission to the beach. The beach is huge and though it is very crowded by the parking lot and buildings, if you walk further down there are barely any people and it feels like you're on a private beach. The water was great, but it's just a sandy bottom so there isn't much if anything to see if you bring snorkel gear.
Due to impending rain all day and rough water, we chose to stay on board during our Half Moon Cay day. Four members of our group did spend the day on the island though and they loved it. The beach is huge and they said that it was the best beach that they have ever been to. They even liked it better than Magen's Bay and Trunk Bay. They said that the walking trails were great and that the facilities and island overall was very clean.