St. Thomas save yourself the money. The skyride is right across the street from where the boat docks. You can get off the ship and walk across the street and pay there (it's alot cheaper). However, it not much there (minishopping area, parrot show, but great photo opportunities). I would suggest if you like the beach to catch a cab to Magan Bay and if you like shopping - the shopping area is a nice walk from the ship (don't waste your time on a cab to go shopping).
Dominica - We took the 4x4 jeep ride and that was wonderful. They took us to some of the beautiful sites there (excellent photo opportunities) and then we went for a swim at a certain location but it was excellent. To me that was worth the funds.
Barbados - Is a great place to take a tour, however it's not recommended that you go off on your own. I did the coast to coast tour as well.
Aruba - I did the tour years ago but I don't remember to much about it. However that last time I went to Aruba - we caught a cab and hung out on the beach and had a great time. There's also a shopping plaza not far from the pier - walking distance.
St. Thomas, havenīt done Sky Ride, but heard, thats too expensive.
Do your own tour, ask a tyxi dispatcher close to port, go together with another couple and you can make an island tour for half the price as the ship excursions.
Aruba and Barbados do it also on your own with a private cab, about 20 $ per person, much better than the crowded bus tours.
Dominica: havenīt been there.
In almost every port are people from the tourist office and they can give you advices for good and not too expencive tours.
In st.thomas I would recomend a private tour with sunnylistontours.com . 20dollars per person. He picks you up at the pier btwn9am-11am(you choose the time) and takes you and drops you off in town to shop untill noon. Then he drives you on a tour of the island for approx. 1.5 to 2 hours,including to the the top of the mountain.Then he drops you off at Coki or Sapphire beach to swim or snorkle or just have a bite and a drink and relax.Then picks you up and drops you back off at the pier. You don"t pay till the very end.
I am sure have posted some ops before, but here goes.
St.Thomas no excursion is required, study up and take a taxi where you want to go. Taxi's here load up all they can in vans and charge all. I highly recommend Megans Bay for first timers to get a feel for the island, though not great for snorkeling. To really see the islands..get off the ship early and take a taxi to Red Hook, board the ferry to St.John, then jump on back of truck/taxi to Trunk or Cruz Bay.. and snorkel you will never forget it, and will get an extra island in.
Dominica, A shore excursion is required on this island. It is quite different, of my 2 visits I personally reccomend..take the tour of island you will be shocked at the poverty, or if you snorkel take the one that does off-shore, great crew and very informative and attentive for safety. The vendors will be waiting for you at end of pier.
Barbados, Beautiful waters, I took an excursion that left from a good walk up the pier that went out and we snorkeled over a sunk ship..was pretty good..I did not get to go on island.
Overall, the only one to go off and do your own thing is St.Thomas
Revising Post: I did not see Aruba on your list!
Did not go on excursion, went over to Sonesta's private island/beach. I called ahead and asked and they had tickets for me waiting, expensive 10oz beer, and lots of Iquanas, but pretty water. I can say was pretty safe to walk around, and casinos etc you can walk to safely even at night was my experience. I will tell those that are keeping up with the Natalee Hollaway story that the ship will dock right there at Carlos N Charlies.. Have a wonderful cruise! Island