If you can get a good tour independently, it is usually a better deal. On our upcoming trip we have booked a full day in St. Thomas through Godfrey Tours. Put him in Google and it will direct you to the website. Shopping in the a.m. and sightseeing and/or beach or snorkeling in the afternoon for $20.00-$25.00 per person.
You have no choice in Princess Cay. You are a captive audience there. We are going to rent a cabana--that's about it.