Best Caribbean Destination from Miami in October?

Looking at a 5-10 day trip in mid-October (timing firm) departing from Miami; direct flight preferred. We're a couple looking for a relaxing and romantic beach trip. We are scuba divers so that might be a factor, too. Budget is $500-$750/night.

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I'm looking for recommendations for (1) destinations and (2) resorts. We've already been to: Mexico, Belize, Cuba, Puerto Rico, Dominican Republic, and Jamaica--it needs to be somewhere we haven't been. Thanks!