The lex line is great, all those IRT trains really fly. Also the D train is pretty good once it gets north of 42nd Street. We used to take it to Yankee Stadium all the time. You can get there in a flash.
The NYC subway system is a great system of Mass transit. I hear things are even better in Europe, but I wonder if there is a better system in the US. One thing planners elsewhere would do well to remember (Hudson-Bergen Light Rail people and NJT Bus Operators, I'm talking to you) is that to be really an alternative to cars mass transit systems MUST run 24 hours a day.
I've never actually visited Los Angeles, but supposedly they have a pretty decent system of mass transit.
Unfortunately, not many people use it, so it serves more as a massive public spending boondoggle than an effective way of transporting people from one place to another.
Also, the way Los Angeles is mapped out is vastly different from New York.
I suppose that it's easier to commute long distances by car in L.A. Then again, I've never been there, so I wouldn't know the specific logistics involved.
The lexington avenue is great but so is the 7th avenue line. Now, though, due to the bomb being set off in the Times Square stop (supposedly by a crazy cop but who knows), I'm reluctant to use it at all.