I can give Koh Chang Divers my higest recommendation. My wife and I had our first vacation to Thailand, and started out in Koh Chang in Bang Bao. After looking at all the dive shop we selected Koh Chang Divers, due to the cosy atmosphere and warm and honest welcome from David and Mike. David, (whom we off cause named Jacques Cousteau when talking about him), started to suggest us not to dive the first few days, due to bad visibility. That impressed us.
And we didn't get dissapointed. Never had so cosy and relaxed diving, sailing and company. We will get back again.