Use economies of scale. If you're traveling with several co-workers, taxis start to make sense in places they wouldn't otherwise, since the incremental fare per person is minimal. Consider your back. Public transportation, while often the best bet, should be ruled out if you have much baggage to lug. Stick with the licensed.
Many cities advise against using unsanctioned transportation, such as unlicensed limousines.
Travelers run the risk of being swindled or victimized, with little recourse. Invest in information. Salk International's Airport Transit Guide is a pocket-sized book that includes extensive transportation data for 451 airports in the U.S. and around the world. Another choice is How to Get Out of the Airport by Howard Wendland. Then board the water shuttle to Rowe's Wharf, next to the Boston Harbor Hotel.