You probably won't be diving 'the' U.S. Virgin Islands in one trip; you'll probably dive
one. St. John has a reputation (judging from online posts) for good snorkeling, but doesn't seem to be a popular dive destination. So you're picking between St. Croix and St. Thomas.
Did a family trip to St. Croix in 2017, and stopped one day of a cruise years before.
St. Croix Research Report Aug. 2017 -
St. Croix Research Report Aug. 2017 Long story short, good trip. Hopefully I've provided the info. you need, aside from the fact my trip was pre-hurricane.
Been to St. Thomas on cruise ship stops a few times; dove twice, 2-dives finishing up OW cert. on referral in 2006, 2-dives for fun 2012. They picked me up at the pier, fun, so good and comforting that my wife (who dove in 2006) was put at ease and had a positive experience (not always easy to accomplish); don't recall named sites in 2006, but in 2012 dove Armando's Paradise and Navy Barges.
My impression of diving from the very small sample size of 4-dives; roughly 40 feet deep over flat bottom, roughly 50 foot viz., some nice reef and decent life, warm water and current wasn't a problem. The shoreline is beautiful in places, viewed from the boat.
Topside, they drive on the left. St. Thomas is a big deal as a shopping center in the Caribbean, and a major cruise ship port, so there's lot's to buy and a lot of topside excursions to choose from. We visited 'Coral World' on one stop and liked it. On another we took an excursion to visit St. John.
I seldom if ever see trip reports for 'dedicated dive trips' on ScubaBoard where someone spent a week in St. Thomas
just to dive. Plenty of discussion related to cruise ship stops. I liked the diving in Key Largo better (again, 4-dives is too few to judge St. Thomas well).
Since St. Thomas seems to offer so much topside and good diving, too, I wonder why it's not featured in more dive trip reports here.
Richard.