A:It depends on the citeria. Tokyo's system coverage is excellent (80% of residents can get to a station in less than 10 minute. walk!), the stations in Hong Kong are the most convenient, in NYC the service around the clock is the best, the general layout in Paris is excellent, Moscow's system is the most punctual... But overall I would say Tokyo.
It is extremely crowded, though. I'm not sure I would enjoy using it.
