Of course, train is the most popular mode of long-distance transportation. It has four bunks, teacups, sheets and blankets. Males and females may be together in one compartment. It's comfortable, but the bunk may be a little cramped for the average American man. Trains often leave in the evening and arrive at their destination in the morning.
Hard sleeper is the next step down for overnight travel.
The sleeper berths are not bad, from what I've read and heard. Soft seat and hard seat are the other options. The main attraction of soft seat, as far as I can tell, is that you don't have to be crowded in with the proletarian masses in the hard seat car. We traveled hard seat on one short trip from Shenzhen to Foshan in Guangdong Province. The biggest problem here was getting on the train.