We walked to and from El Morro, had planned to take the Trolley but it was always full. Taxis wanted way too much $$ for the short distance. It was a rigorous walk but ok for 2- 30 somethings and 2 elementary aged kids. Places to stop for drinks along the way.
El Moro was nice and we enjoyed it.
One port of call to San Juan is all you need, I would actually not pick it if you can avoid it.