You've got a very apples-to-oranges comparison going.
1.) Little Cayman's Bloody Bay Wall and Jackson Bight strip has been held out as amongst the best rec. diving in the Caribbean, with Cayman Brac. very close but trending a little deeper (plus offering some shore diving). But these islands aren't known for a hopping topside.
2.) I thought the outer atolls region of Belize was similar in overall quality to Little Cayman, albeit with less personable wildlife, but that was via live-aboard, and not everyone gets to hit quite the same places.
3.) Bonaire is great if you love the independence of shore diving. Of the main west coast stretch, I do think the far southern sites have the lushest, best looking reef (and Karpata way up north rocks, too), but Bonaire isn't known for reef sharks or as a big animal destination (but it has green morays, tarpon, barracuda, cubera snapper, some sea turtles...), and shore diving it some work...not 'valet diving.' You can get that sort of experience, say by hiring V.I.P. Diving I hear, but professionally guided diving isn't what seems to draw most people to Bonaire.
4.) Cozumel - good diving, good food topside, has various topside entertainments, overall trip costs can be budget friendly. Some people like drift diving and some people don't.
5.) Grand Cayman can be pricy, but airfare and car rental are reputedly pretty good. It's a cruise port, so topside excursions are available, and some places have shore diving.
6.) Trip reports on the Bahamas tend to compliment dive op.s but suggest the reef can be underwhelming a bit, possible exception being the Juliet's route. Worth doing a forum Search and reading some trip reports on that.
Some follow up questions might help:
1.) Do you want to do much (if any) shore diving?
2.) Do you like to stay 'on the reservation' mostly, at your resort, or roam around the island?
3.) How many dives/day do you want to do?
4.) How important is it to see a few reef sharks?
5.) Have you traveled to dive in the Caribbean before?
6.) I take it you plan a land-based trip, not a live-aboard?