We just got back from 9 days in Puerto Rico. Definately rent a car, price is very similar to the mainland US, and you need it to see anything. We enjoyed seeing El Morro and learning a bit of the history. The Rainforest was ok, was more of a cruise ship excursion. If you haven't just returned from the BVI's or USVI's you might want to head over to Culebra for the day. I flipped through the lists on Tripadvisor to find things of interest. By the way, the security line was rather slow at SJU, took an hour to get through. Usually we are in the Precheck line, but they wouldn't let us, something about the way I checked us in. We had a great time, have fun!