There's great snorkeling all over the Bahamas, but we haven't found any island that compares to Eleuthera as far as access to snorkeling sites from the beach is concerned.
We've visited Bimini, Cat, the Abacos, Little San Salvador, Grand Bahama, the Exumas, Andros, New Providence, and the Berry Islands numerous times, and haven't found any that compare, unless you've got a boat.