Cayman Brac, Turneffe, Cozumel. Unfortunately, South Caicos no longer has a dive op, otherwise it would be number 1 or 2 based on diving. Deep walls with schooling sharks and or eagle rays. The island is not set up for tourism. Cozumel has great vis, good sea life, but the second dives tend to be farther north and those reefs are not in good shape. Turneffe, visibility is ok but not like Coz or the Caymans. Good sea life. Great snorkeling in the lagoon. I put the Brac over little because it has better corals. The south side walls are deep, 55’ to 80’ at the top of the wall, but the corals on them are good, good sea life, and one usually see a shark. My wife prefers Little Cayman.
Honorable mentions: Key Largo ... good reefs, good sea life, lounge boat ride making more than 2 dives hard to fit in. Utila.... great variety of diving. Sea mounts, wall dives, muck dives, piles of sea horses. Over fished so grouper and snapper are rare.