Bahamas - The reefs here seem to form themselves into tight coral heads. Each bunch grows up from the sandy bottom like a flower. The best snorkeling (in terms of quantity of fish and other sea life) was found inside the Warderick Wells National Park, where a fishing and harvesting ban is strictly enforced.
San Blas - The best snorkeling was found around an old shipwreck in shallow water. A wide variety of fish and coral had made their home on the old steel boat. The size of coral growth was smaller than in the Bahamas, however it was much more colorful.
Tuamotus - The perfectly calm water inside the atoll provided some exceptional sight-seeing. One coral ledge we snorkeled had some very colorful giant clams (about 4" wide), however the colors of the rest of the coral seemed muted. Some coral heads here grew from the bottom like giant chimneys, making navigation particularly exciting.
Moorea - The fringing reef we anchored inside had some interesting formations (as well as a few black-tip sharks!), but the diversity of coral was rather limited. It was, however, my first sighting of a wild clown fish (ala Nemo).
Great Barrier Reef - As Captain Ron proclaimed: "Huge! Ran the whole coast." The reef is indeed huge (although not necessarily continuous), and everything on it is similarly large. We saw giant clams (large enough to fit a small child inside), massive sea fans, parrot fish the size of watermelons, and an impressive variety of colors and coral species. At our last mooring, we tossed some moldy bread overboard and within seconds, a flurry of colorful fish were fighting over the scraps (including two fish the size and shape of a trashcan lid and one ugly, brown fish the size of a German Shepard - sorry, I still need to do some research to figure out the species).
Coral reefs throughout the world have certainly been beautiful, exciting, and marvelous. In my opinion, they're a resource certainly worth protecting - even just for their sightseeing value.