I've been to Bonnaire and Coz.
Bonnaire pros:
The reef is amazing. Much better shape than Coz. Far enough south it misses most hurricanes. Most sites we dove were so dense you had to look for the sand.
The absolute freedom of shore diving.
No current. When you find something interesting, you can hang there and watch as long as you like.
Good viz.
The reef spans the entire length of the island, starts at 12fsw and drops as deep as you want to go. Your safety stop is on reef most of the time, and since there's no boat waiting, you can poke around in the shallows a long time draining your tank. Bottom time, bottom time, bottom time.
Good food.
Cons:
Expensive food.
All-day affair & $$$ to get there from most places.
Shore diving is a lot more work. U take care of everything.
Don't leave stuff in your truck. And don't lock the doors, that's an invitation.
Cozumel pros:
Great Coral formations.
Drift diving; cover more territory
Effortless, spoiled diving, depending on the op. I use Blue Magic Scuba; they take care of EVERYTHING.
Better variety of fish.
Good viz.
Good food.
Cheap food.
For me (Chicago area) it's the cheapest & easiest dive destination to get to.
Cons:
Drift diving, sometimes the current is stiff, and I like to poke around.
No realistic shore dive option. I like the freedom, and it's cheap

A little cooler in winter.
FWIW, the clearest water I've been in was Grand Caymen. On the deep wall @ 140fsw I want to say it was 200', but that's so much farther than anywhere else I've seen, I'm not sure how to judge it. Other than that, the diving wasn't as good as Bonnaire or Cozumel, and everything was pricy.