I've been to Grand Cayman and Aruba, none of the others so I can't speak to them. I liked the beaches better in GC than Aruba. Dont get me wrong, Aruba has some nice beaches, but Aruba is very very windy, all of the time. GC not so much. Crime, not so much on either island as far as I can tell. No one really coming up to you etc on either island. Cayman is very safe. Now the snorkeling is hands down better on GC than Aruba or any of the other places you mentioned, for one, there is no real current to contend with, and water temp will the around 80 all year around, a little higher in the summer, a little lower in the winter. I was in Aruba in the winter, and it was around 78-80. Plus you will see more in Cayman than Aruba, plus you dont really have to sign up to go with a tour group (you can if want) just start swimming and you'll find plenty to look at on GC. That said, I'd definitely take a snorkel trip to Sting Ray city, well worth the price.
Aruba has gambling, GC does not.
I am going back to Cayman, would I go back to Aruba? I think I would like to try somewhere else first.
let us know what you decide!