We did the Charlotte Amalie walking tour. It was interesting, and a nice day if you don't want to go to the beach. It's actually only about a 2 hour tour, woth two hours for shopping afterwards, so you would have time to do taht and the beach if you wanted.
We liked it as we got a taste of the history of the island.
If you do it, be prepared. There are stairs. Luckily you walk down all but a few, but this is not a good tour if you are mobililty impaired, and not at all accessible. Also, at one point you will stop by a bunch of trees and there will be iguana's in them, they sometimes pee and poop out of the branches. I got "christened" by one.
Anne