Vietnam forum

I've never taken the bus, but I thought the overnight train was a good way to go. You get on, go to sleep, and in the morning you're in a new place without wasting a day getting there. It's four to a cabin and pretty comfortable. You get your own bed, no sharing. The train cars can be old and rickety though, bring earplugs.

Beware the friendly local who will "help" you load your baggage into the upper compartment when you get to your cabin. That help, of course, will cost you a small fee.

I recommend just going to a travel agent to buy tickets, it may cost a bit more, but the Hanoi train station is a zoo and half the time the sleepers are all sold out anyway (the travel agents buy them all up).

I've done the Hue/ Hoi An /Hue trip many times, by big tourist bus, min bus and train and would always get the train by preference.(the station is actually at Danang not Hoi An) Not only is it more comfortable, but the scenery is great. It's better on the east side but even the other side is good. You don't need a sleeper for this segment as it only takes about 3 hours (and costs $2 or $3). You can buy a ticket just before you catch the train at Danang, or Hue, station just before you get the train. I've never been able to get a ticket ahead and once even scored a last minute ticket just before Tet.

You will need to get a cab or bus between Hoi An and Danang, but you can use this trip to call on the Cham Museum at Danang (arrange beforehand for your cab driver to wait an hour for you here)

As for sleeper trains generally, you share the cabin with 3 others. I've found that they'll generally put you in with other tourists, though I have also shared with locals and never had a problem. Actually I've found locals generally quieter and earlier to bed, which suits me. You'll get a meal and a rudimentary breakfast, water and bedding. Boiling water is available at the end of each carriage and people come through regularly selling tea and coffee and snacks.
Check seat61.com for timetables and more information.

For what it's worth, I found the train from Hanoi to Huê was really convenient this summer. It leaves around 11 PM and arrives in Huê less than 12 hours later. It was quite comfortable and I slept very well. One way was around 500k Dong and of course one night less of hotel expense.