I just came back from Bonaire. Diving-diving-diving. Not much else to do. Night life is very little, one bar in downtown by peer serves alcohol to Dutch speaking teens. Some locals there too. Beaches are not that great, not easy to get in and out. But water is clear and very warm. Reefs are the best I've ever seen. Coz has nothing on Bonaire. Don't know about Roatan or Belize.
But for non-diver Cozumel would be the best. Depends how many dives you planning you can stay either on mainland or on the Island. They have some very good AI hotels with sandy beaches. Beaches are better on mainland, but people say Allegro on Coz has very nice beaches too.