I was in St. Thomas a couple weeks ago with a friend of mine and dove every morning with the crew of St. Thomas Diving Club. All of the dives were fantastic, despite having to deal with the remnants of Hurricane Tomas. We saw sea turtles, lobsters, conch, spotted ray, brittle star, barracudas, octopus, nurse sharks...and thousands of beautiful fish. If you go, be sure they take you to the "Cow and Calf" dive site. That has to be my all time favorite!
All of the staff there are fantastic, friendly and helpful with any questions you may have about scuba diving. The shop has everything from BCD's to T shirts...so anything you need is right there.
I am going back in January for a wedding and you can rest assured that you will see me on the LETTS DIVE boat every day!! Highly recommend that you try them out!