all classes. If you have an "open seat" and it's rush hour, there might actually not be a seat for you.
The mass transit is really easy to navigate. I used the webpage for the train, and it gives you a barcode you can use on your phone for the ticket. It was really simple.
When in the city, I just bought the 24-hour pass and kept it in my wallet (I was never asked), this allows you to use all of the inter-city mass-transit by just walking on.
This was quite nice compared to Korea where you had to have a ticket or pay change for every bus and subway.