These are the metro (subway, underground) systems I've ridden. OK, I rode one (Pittsburgh) all of one stop, but a system's a system. I rode two (Cleveland and St. Louis) because I attended the respective Revival conference of the Unitarian Universalist Christian Fellowship. But a system's a system.
[The service that served the subway logos is gone.]
Of course, the best system is the one you ride the most; for me, that's Washington Metro. Moving from private car ownership to public transportation -- whether rail, buses or ferries -- and walking is an important contribution you can make to reduced energy use and tighter cities.
Hat tip: Doctor Transit