Although I'm not a peak rush hour user, I love Seoul's Line 9. It has the best logo, the best station arrival jingle, and the stations are generally clean and sparkling new. Sinnonhyeon station, right in the middle of Gangnam, curiously has an entire unusable mezzanine/cavern level that you pass every time you take the escalators down to the tracks. Seems the station was overbuilt for capacity, but the line itself can't support more passengers.

A public/private partnership seems more the way to go: municipality funds development of the line but lets private sector entities operate it according to agreed-upon standards and performance objectives. That's the way it works in Stockholm, Hong Kong, and many other cities. On the other hand, if it's all publicly operated, then what's the incentive to keep improving things since your only stakeholder is the public and you're a monopoly anyway.