I've never been to Little Corn Island, so I can't compare it to Jamaica. My first question about it would be: how and how much to get there? It is one of the places I have on my list to someday visit, though, along with a few other islands off Colombia and Venezuela. I snorkel and scuba dive, and much prefer to visit places that I can snorkel from shore whenever the mood strikes me. My favorite these days is Dominica, but it requires a couple of air connections to get there, and it has no beaches in the usual sense. Great rivers, mountains, and rainforest, but almost no tourism infrastructure.
Jamaica has some turtles; I've seen small Hawksbills early in the morning only a few feet from shore. They are fairly common along Negril's cliffs, at dawn. There are loads of Morays everywhere there is cover for them. Rays are also abundant. Rays come inshore over sandy bottoms at dusk to hunt for shellfish, etc. Some are huge. What you will not see in Jamaica are bigger fish that are caught by fisherman in fishtraps. Rays and Morays are not sought as food, and usually cannot be trapped, so they are common.
Generally speaking, anyplace you go, big beautiful sandy beaches will tend to have limited or no inshore snorkeling. Look for rocky areas, cliffs, projecting headlands and points, shallow water, moderate currents and light wave action on an island's lee side. In many popular beach destinations shallow inshore coral structures are deliberately destroyed to eliminate urchins that might discourage tourists. Some places, like many of the Bahama Islands, Turks and Caicos, etc., have very few coral reefs that are easily reached from shore, just like in the Keys.
