If you are looking for something more low-key, I highly recommend Heron Island which we visited years ago and they have updated the small resort since then. I believe it is actually an atoll and we took a helicopter to reach it. The diving/snorkeling were superb and we liked the fact that it wasn't glitzy, just a more natural experience. There have been articles about it in T & L and Conde Nast Traveler magazines. The fresh Bay Bugs were delicious too!