don't bother going to the BVIs or St. John or St. Thomas for a dive trip, you will most likely be disappointed. there are a few decent wrecks, but aside from that, it's pretty boring. I've spent a lot of time sailing over there, and always stop for a few dives along the way just for something different, but have never been impressed (the wreck of the RMS Rhone is not nearly what people make it seem). St. Croix, the red headed step child of the Virgin Islands, however, is GREATLY underrated. going on 1000 dives here on STX, and have yet to get bored. super healthy shallow reefs and amazing wrecks on the west end, one of the best walls in the Caribbean along the entire north shore, and Long Reef, one of the longest continuously living barrier reefs in the Caribbean also on the north shore. We have had divers dive with us for 3 weeks straight and never dive the same site twice, and they are all unique. oh, and St. Croix is also FAR less expensive than the other islands, way more laid back, and our economy is not tourism/cruise ship driven, so you get a very different experience here than almost any other island in the chain.
hope that helps