The train I went down from Hanoi to Hue had the splendid name Reunification Express 3. I checked in early enough in Hanoi, that I could take some nice pictures.
The soft-sleeper cabin consisted of 4 berths. Well the mattress was harder, and because it is warm normally in Vietnam we only got a thin blanket. For that night it was much too thin we had heavy rainy weather outside and only 13 degrees. It was really cold on the trains.
So the best train sleeper award on this journey goes to China Railways. Mattresses are nice and you get thick blankets. And railroad lines are better maintained than in Russia or Vietnam.