They are usually well-maintained, late model Japanes cars, like Toyota Corollas, and you have the added advantage of having some degree of control over how your driver operates the vehicle. If a car is not in your budget, the next best bet is minibus. Japanese-built and often brand new, the only negative is the drivers are usually intent upon breaking all previous land speed records. Personally the only use we've found for public buses in Vietnam is as mile markers - there's one broken down every other mile. Whatever transportation you choose, you'll have the privilege of sharing the road with bicycles, pedestrians, oxen, water buffalo and trucks straight out of a Mad Max film.
Road conditions vary from poor to unbelievable.
That's the good news. The bad news is all the other obstacles you must contend with. I once showed a friend a picture of children playing. If you spend any time here at all, you will witness accidents. With a little luck you won't be in one.