In the past we went with Dive Safari's based out of the Scuba Shop in simpson bay. (Near the bridge, lagoon side.) We did a refresher course, (we hadn't dived in 5-10 years) and had a great group dive with two dive masters. One DM was certifying 3 divers as rescue divers, and the second DM guided me and my wife about. Great fun and very personal service.

They do their initial checkouts in a pool on property and then hop right into the boat for open water and fun.

Also if you are staying at the SBR, they have great snorkeling right in front of the beach. Swim straight out about 100 yards. You'll know it when you get there. ;-)