The amount of areas serviced (even acknowledging the subway desert neighborhoods) and 24 hour access, to me, is the distinguishing feature that makes MTA the most convenient. I've never been to London, but I do visit DC often and use the metro. Coming home after seeing a show at echostage, or going to a bar with friends, the metro is not an option. If I'm staying in the sorta equivalent of the "outer boroughs", the metro is not an option.

I'm also wondering if the Nats have a late extra-innings game, does the nearby line run a few extra trains past the last scheduled train of the night? I'm guessing not, but am curious.