I've used both Dolphin Water Taxi (they have private trips too, https://www.dolphinshuttle.com/) and Platinum Yacht Charters (http://platinumyachtchartersbvi.com/).
Dolphin is much cheaper, but PYC is really travelling in style. Dolphin operates smaller power cats with outboards (usually just one) and its a pretty barebones trip, PYC was on an Azimut 55 and was top quality with beer, wine and a hostess, but you pay for it.