The airport is just beautiful and of course is linked by train to the city. I have a good friend who lives there. Three different bus lines run near her parents' home. All of the bus lines link to the local train station. The system is incredibly clean and safe. I was able to go all over the city with ease. The trains and buses always run on time. The city is so beautiful. There are excellent roadways and highways too. It is all very safe and efficient and well designed.

the two systems, S-Bahn and U-Bahn blanket the city and suburbs, are modern, have short headways and are well linked to rail and air travel.

Berlin-I'd make this #1. The U-Bahn and S-Bahn cover the city and surroundings pretty well, but there is also a really extensive light rail system with frequent service getting you everywhere in between.

Prague's system and area is smaller but they cover it well with subway, streetcar and buses that seem to get you everywhere quickly. The system's monthly pass is a bargain. The system is also well linked to the rail network.

Toronto-I thought the comprehensive subway system combined with light rail lines on most thoroughfares above ground (that have frequent service) meant that you could get to most places within the central and inner ring very quickly.

Never been there myself, though. I wish there was some sort of quality index for mass transit systems, based on universally agreed criteria (percentage of homes within 500m of a transit stop, frequency of service and so on).

This site has many pictures taken in panoramic view of the Moscow Subway:
... http://www.beeflowers.com/moscowmetro/index.htm

Here's a youtube video.

If I lived in Toronto and my home/workplace were in any way accessed by their mass transit I'd use it in a heartbeat. Clean, efficient, and the buses pull right into the train station, which allows you to pay once, even if you make several connections. And it's relatively affordable.

DCs metro system is costlier, you have to pay when changing from subway to/from bus, and it can take 2 hours to get from one side of the system to the other. When I used it (I used to commute from the 'burbs to downtown) I did a cost comparison, and even figuring in wear and tear on the vehicle, driving a car was cheaper, often faster, and left me with more flexibility. The single advantage riding metro had was that the time it took was more consistent. I hear they are about to raise their rates yet again. Glad I don't depend on that.