We loved the diving off of Playa Santa (Guanica).
I felt that the Black Coral along the wall rivalled any that I have ever seen.
We dove with Island Divers, who we would place at the top of the list of customer service-oriented dive ops. We stayed in Playa Santa, which is quaint, but probably would stay in Guanica (about fifteen minutes up the road) if we went again.
Second choice would be La Parguera, although with three days at Playa Santa, and only one day at La Parguera, can't say we have the full experience at La Parguera.
We dove Desecheo out of Rincon, with Taino Divers, and notwithstanding having to participate in the loading of the boat from the shore, we would do it again. Diving with them two different days, with weather changing between them, we dove the regular (South) side first, and then the less dived North side next. Two totally different experiences, with different structure (and unexploded bombs).
And some pretty cool looking Staghorn coral.
Can't say that we would go through the effort to get to Culebra again to dive (with or without BCD's and wetsuits - and I downsized from by normal 5mm BARE to an older 3mm just to try to make flight weight). While it was good diving, we can find equal diving in the Riviera Maya (with a lot less effort).
Our vacations usually involve a combination of diving and site-seeing, but we have concluded that, if we were to take a non-diving trip, we would put Puerto Rico right up on the top of the list. The island offers so many features that it is worth it to just fly in, and leave the dive gear at home. We love Old San Juan, and find that to be the primary reason we want to go back.