I know this is not popular on this site, but we always pre-arrange our transfers. We us Marjorie Smith with Island Magic. magicplace@hotmail.com
It saves, to us, a significant amount of money. We book round trip. Transfer from STT to ferry, ferry to and from Road Town, (TMM provides ride to and from there) and then from ferry to STT or for us whatever hotel we stay at for the night. If we arrive early we get on the first ferry, and if we are a little late, we get the next one. On the way back we have several times to catch a ferry. This service is $94 per person. Does not include $10 exit fee from USVI or $20 exit fee from BVI. Maybe we have been lucky, but so far so good. Enjoy