I live in New York City and refuse to ride the substandard subway systems located elsewhere in the United States. The majority of the places I visit in large citites in the United States are not convenient to mass transit. Besides, cities in the United States for the most part are designed for and cater to drivers.

In Europe, it's another story. I make use of subways whenever possible as the majority of large cities have efficient mass transit. The ones I've used that I can think of offhand are: London, Paris, Brussels, Prague and Moscow, all of which were fast and efficient and the most efficient of which was Moscow.

I never base my decision to use public transit on the cost of it. I base my decision on convenience. If it's more convenient to take a taxi or drive then I'll forego public transportation.