The bus does it in nine hours. The train does it in nineteen and costs slightly more. I take the train, and I have taken it enough times now to have stopped pretending this is a rational decision about transport.
What the extra day buys
You can walk around. This sounds trivial and it is the whole thing — nineteen hours in which you can stand up, move to a window, go and get food, and sit somewhere other than where you started. Nine hours in a bus seat is nine hours in a bus seat.
You can also work. I have indexed an entire chapter on a train and I have never managed a coherent sentence on a bus. A table, a plug, and no motion sickness turns dead time into working time, which changes the economics completely if you are self-employed.
The compartment
Four berths, and you will share with three strangers. This is either the best or worst part depending entirely on luck and on whether you can sleep with the light on. I have shared with a family who fed me for two meals and refused payment, and I have shared with a man who took a phone call at 3am and then another at 3:40.
Lower berths cost more and are worth it. You get the seat during the day; the upper berths get a ladder and a ceiling.
Where the argument fails
Trains only go where there are rails, which in most of the region is a thin and inconvenient network running mostly north to south. Half the journeys I want to make have no train at all, and a route that involves two trains and a connecting bus is worse than the direct bus in every measurable way.
Take the train when the train goes where you are going. Do not build the trip around it. I have made that mistake and spent a day in a junction town for the aesthetics of it.