My thoughts...

Snorkeling around the Seven Mile Beach area is OK. Corals are pretty much wiped out, but you can often see a nice variety of fish and occasionally turtles and rays. Water is usually calm with little wave action.

Cemetery Beach on the Northern end is one of the better spots. The less damaged/destroyed corals are 150 yards or so from the beach.

Governor's Beach in the Central beach section has a small patch reef and lots of fish (unfortunately they are used to being fed by snorkelers).

The rest of the snorkeling spots are located in George Town. With Devil's Grotto/Eden Rock being the best, followed by Cheeseburger Reef and wreck of the Cali. Wreck of the Gamma is not so great.

The snorkeling off where you are staying can be OK as well.

Also, past the Northern end of SMB and into West Bay is Turtle Reef off from MacaBuca/Cracked Conch restaurant. OK for a deep water snorkel (really more of a dive site).

The mini-van buses of the #1 Yellow and #2 Lime Green routes run up and down West Bay Road from George town up into West Bay, just flag them down from the side of the road and tell the driver where you want to do. They should know each stop mentioned above. Pay when you are getting off.

Buses will be crowded at rush hours and if there are lots of cruise tourists in port. You can of course carry on your belongings.