I love Grand Cayman and the diving is definitely easy and gorgeous and meets your criteria. However, it is also a costly option (more costly). If I had to pick 1 place only, I would select Bonaire. So much so, that I am taking 2 of my very best friends there next month. They have a grand total of 40 dives combined and I chose Bonaire as the most favorable location for them to get in lots of dives and improve their diving skills, at a reasonable price, with very easy diving conditions. Even if all you did was boat diving, which you don't want to do, the cost of boat dives in Bonaire is 1/2 the cost of Grand Cayman. My 2nd choice would probably be Roatan and Coco View Resort or Anthony's Key Resort.