We went to Athruga a couple of years ago and couldn't recommend it highly enough. It is right on the reef, so the snorkeling is fantastic and the service is next to none. It is / was run by an Italian company called Franco Rosso, so the food was plentiful and excellent. The staff couldn't do enough for you, even getting me down a coconut from the tree when I fancied some.
The island is one of the smaller ones, taking only about 10 minutes to walk around and doesn't have all the amenities that some of the larger resort islands do, but it makes up for it in so many other ways. I swam almost the whole way around it one day, accompanied by a turtle. Luckily I had my underwater camera with me as it was one of the most exciting moments of my life. We also saw oriental sweetlips, numerous parrot fish, sea urchins, loads of different trigger fish, sharks and more than I can remember right now and the seaplane transfer just made it all that much better.