I've done Hawii snorkeling, Virgin Is. snorkeling, and Flordia Keys snorkeling. There is absolutly no comparison, the Virgin Is. If you want to go somewhere you can see tons of different corals, fish, inverts, then goto the Virgin Is. I went to St. Thomas, and stayed at a place where we had the beach to ourselves.
There was a bar right on the beach, so you could drink then snorkel, then drink some more, then snorkel...
The reef was completly protected from the elments, and the area of the reef was probably 2-3 acres. The water was 80 degrees, and perfectly clear. You could see the bottom perfectly at 100 feet.
Snorkeling in Hawaii had little coral, but lots of fish, the water wasn't as clear, and it was very rough to swim in.
Snorkeling in the keys, you really have to watch out for the baracudda. Once while swimming there I found myself completely surrounded by cuda's. Ranging in size from 6 inches to 6 feet.