In NYC I tended to feel safest around cabbies; they're accustomed to the local traffic patterns (including the presence of bikes), and unlike out-of-towners they're not distracted by probing unfamiliar streets or searching for parking spaces. I'm warier with Boston cabbies, from whom I've seen a lot more instances of aggression and general inexperience.

Buses, of whatever type, however, make my blood run cold. Put a bike lane on a major city-bus route, and watch the sparks fly.