I was clearly out of it yesterday morning, as I forgot to include the city I live in.Ranking the ones I've experienced:
1. London: The Tube, as many have mentioned, appears to run well most of the time. Though there are delays at times. Most of the city proper is fairly well-covered. I've heard good things about the buses, but have only tried it once in my 3 visits. I also took a train to and from Brighton that was very convenient.
2. NYC: Great coverage by the subway system in Manhattan. The PATH train is also handy for getting onto the island if you're staying in or near Newark. You can also get to lots of different places in NJ by taking a train from Penn Station. And I've taken the LIRR (Long Island Rail Road) from Penn Station to eastern Queens and back for a TB get-together. Oh yes, and I should count the Staten Island Ferry--it's free and you get a great view of the Statue of Linerty.
3. DC: Limited experience, but it was easy to use, and the long escalator coming out of that one station was pretty cool.
4. Amsterdam: Only took one round trip. There was nothing inherently wrong with it, but we were told you could pay on the train and we never figured out how to do that. So we ended up riding for free. I feel kind of bad, but we basically had no choice and the two rides were pretty short.
It lands in the middle of my rankings.2.5. Chicago: The El is really convenient for certain neighborhoods. Indeed, from my office downtown, it's two blocks or less to trains that go directly to O'Hare or Midway. And the trains generally run on time. The bus system is also pretty strong (though I might be biased since my route stops outside my building and drops me off less than half a block from work). While the buses don't run like clockwork due to traffic, they run pretty frequently in a lot of areas. And the train/bus tracker app on my phone works for every stop in the city. Finally, the Metra commuter trains that run straight to the suburbs (virtually no stops in the city) bring a ton of people into downtown for work each day.