In gerneral the newest, largest boat from the best operator you can afford. In almost every case the mono will be simpliar for the less experienced crew or skipper. To your specific question the new skipper not familiar with sailing distances should use a Tortola base. For those that understand the procedures and sailing distances the flight to boat simplicity of St. Thomas is a joy. The bigger and newer the boat the better. The sailing navigation of Tortola is better. The air and land ingress and egress is better with a St. Thomas base. If you are new to any of this keep the parts new to you simple or as limited as possible. One step or bite out of elephant at a time on your group vacation.