My first open water dives were in Aruba, so I am a ittle biased about that, but it does offer some great mid depth wreck dives, REALLY great viz and little current (except at the California wreck, it is very strong there). Curacao is said to have some great wall and reef dives near the Seaquarium. St Thomas is very crowded and depending on the time of year, strong currents. They say the drift diving in St Lucia is something everyone must do once, I took my wife snorkeling there at Anse Chastenet (that is where Scuba St lucia is). Great volcanic coral, loads of fish and the color on the reefs started at about 20 ft. Barbados has a few good reefs, the Stav...something wreck (at about 100 feet, strong current, but biggest wreck in the Cairbbean) but there are plenty of shallow wrecks there too. I could have spent a week diving the wrecks in Carlisle Bay alone. Only about 45 feet, white sand bottom, very clear, lots of accidental wrecks as well as intentional one's. Great fish life.
If you are interested, I can recommend a good operator in Aruba and one in Barbados so you can avoid the ships dives.
If I were diving on that itinerary, I'd also put Aruba and Curacao on the top of the list. St. Lucia and Barbados next on the list, followed by St. Thomas and Antigua, and finally San Juan (unless you can get to the other side of the island or Vieques (sp?).
The "Stav" wreck in Barbados is the Stavronikita, and you definitely can't do that with cruise ship dives, as it is fairly deep at 100' (deep for cruise ship dive operators, that is), and not advisable for novice divers. But it can be arranged on your own.
If you're just going to dive 1-2 times, I'd go with Aruba and Curacao in a heartbeat.
Great itinerary, by the way - which ship will you be on?