We just got off of Infinity. This was our second cruise on Infinity. We love the ship. Very good food and very nice decor on the ship. (Elegant decor not flashy like some ships.)
We have been to some of your ports on different ships. St. Thomas is very commercialized but still a very nice stop. You can take a taxi to downtown Charlotte Amalie to do a lot of shopping. If you take a tour that takes you to Megan's Bay, you will love the blue water. You can also take a tram ride up the side of a mountain that will give you a great view of the cruise ship. We took an island tour on Barbados and Grenada. Barbados was very nice. Grenada, at the time, was totally uncommercialized and one of our favorite ports.
On St. Thomas I'd say that my favorite excursion was Trunk Bay over on St. John. The snorkeling is fantastic, the Island of St. John is beautiful, and not nearly as congested as St. Thomas, which reminded me of NYC at rush hour..
Did this same route last April on the Constellation, it was fabulous. Our favorite excursion was the sail and swim with the sea turtles in Barbados. We booked through Celebrity and it was agreat day. I agree snorkeling at Trunk Bay is also a wonderful experience and should not be missed. Have a great time.