We've been to PR to dive twice, most recently a couple of years ago.
First time we went, we stayed in Rincon and dove Desecheo twice, and then drove down to La Parguera to dive the wall. On our two Desecheo dives, first day we did the more popular Southwest side, which was okay, but agree that the fish populations could have been bigger. Second day, we dove the less visited Northeast side, where the terrain is considerably different (large boulders, a few more fish, and a couple of unexploded bombs). Then we drove down to La Parguera and dove the wall, and it was simply spectacular. Lots of fish and great visibility.
When we went back recently, we stayed in Playa Santa and dove the walls there. Did three days total, and that was even more spectacular than the wall directly off La Parguera. Great drop offs, healthy coral and fish populations, and sharks and Morays that had obviously been fed Lionfish. I have to admit that Playa Santa, as a town, left a little to be desired, in terms of variety of eateries and alternate entertainment, but I would put those walls up to anything I've dived, including Cozumel.