Mike, there are a lot of them to choose from. I would suggest that if you have a local dive shop near your home, go there and ask them who they would suggest. You could also do an ask.com or google search
They do Sting Ray City & snorkling. Established in Grand Cayman in 1951, is one of the original operators of snorkel trips to the Stingray City sandbar in the clear, warm waters of the famous North Sound.