Snorkeling along the north shore is by far the best off the island. If snorkeling is your aim, it is the place to be. Take a look at the various guide entries like those listed under Rum Point, Wonderland, Queen’s Monument and Barefoot Beach for an idea of what would be in store.
The linked Google Map notes many of the lodging options and snorkeling areas, so you can get a good idea of their respective proximity to one another. Don’t think anyone would consider any of the North Side or East End lodging options to be crowded. Both districts comprise what is known as the “Quiet Side” of Grand Cayman.
The only place where commercial tours frequent is the Rum Point Boulder Coral Garden. But in June there should be few tours since it is a slow time for cruise ships. Regardless, a flotation flag is always a good idea to have in tow. The RedSail water sports desk at the Rum Point Beach Club provides them for free.
If you haven’t already, checkout the TripAdvisor Cayman Islands forum for advice and opinions from others as well: http://www.tripadvisor.com/ShowForum-g147364-i260-Cayman_Islands.html