If we want to see Vietnam in 14 days, should we travel by train or book domestic flights?
TRavelling by air is faster, and a bit expensive!
However, the train system in vietnam is quite good so you can take it as an option. The price is cheaper, but not that much. But it will take a long time.
I think most of the time should be by airplane. Just switch to the train as an experience for short distance!