If you can find the boat you want/need on St. Thomas and you do not mind moving the boat the extra miles? No question St. Thomas is the way to go. If you head to the BVI from St. Thomas(some never leave the USVI) you will be sailing and covering more miles and hours moving the boat. That is not for everyone and every crew. If you do charter from Tortola and attempt to use STT as your airport? I would do the math and consider just how many hours and dollars you will spend to move the entire crew from STT to your dock and back to STT. The $$$$ numbers and hours of hassle can really add up with the STT to Taxi - Ferry - Taxi Dance and return. Usually the key limiter is finding a boat match on STT for your dates. The St. Thomas boat inventory has always been tiny.