I have dived Jupiter, West Palm, Pompano, Key Largo, the lower keys, Little Cayman and Cayman Brac.
In Key Largo, I prefer diving the shallow reefs but I like fish diversity and corals. In the Cayman Islands, you typically get exceptional visibility often at 100' plus. Also because you are diving at or near walls, you can often go as deep or as shallow as you want. The fish populations are very good. You see a bunch of turtles. Also, you see Nassau groupers which are pretty rare any where else.
At Pennecamp, I see even better fish populations than the Caymans. But even here there is fishing pressure even deep within the marine sanctuary. My wife always comes back to the boats with a few hundred yards of fishing line and numerous hooks. I rarely see turtles here. The visibility is decent but it has a marl bottom which gives a milky cast to the water. It depends on what you like. We went out on a boat and the captain took us to a patch reef he knew. It was in 32' of water. It was about 60' long and 40' wide. As I descended, it just looked like rubble. I thought, "What am I getting into?". But as I got down, I started to see really interesting things. My wife and I went slowly and saw one neat thing after another. It took us an hour to just do the perimeter of the reef. Diving is an individual sort of thing, what one person likes, another may not. In the right times, you can see jacks, grouper, and snappers ripping through bait balls. It is really cool.