I think it really comes down to the person traveling.
First of all, renting a car in St. Thomas can be a challenge in itself as there are times when I have been to the airport and there were none available for rent. Secondly, people drive on the left side in St Thomas, so if you are not comfortable with that, you may want to take the taxi route.

However, there are advantages to having your own car as you can go anywhere without having to wait at all. Staying at the Ritz Carlton though, I doubt you would have to wait much to get a taxi as they have taxis sitting right outside so it's fairly easy to do the taxi route.

With regards to additional information about the property, here's a guide that talks about the resort and the surrounding area that might help: Ritz Carlton St Thomas.

Hope this information helps!