We did not book an excursion and chose to walk around the city on our own. We visited both forts. It was extremely humid on our visit so we did not spend much time in San Juan.
The ship docked in St Thomas and we took a ship excursion to St. John. Once there we took a taxi to Trunk Bay Beach. The beach was really nice and not crowded at all.
We booked the rhino rider excursion and had a blast. The traffic was very busy getting to and from the excursion but it was worth it. Be forewarned, everything you take will get wet so you must leave your valuables back at the main building and they did not have lockers. We didn't have any problems but it was not a good feeling to know you were leaving your phone, camera, and wallet back with some strangers. The Celebrity excursion desk told us we would keep our valuables with us and they were wrong.