AChiang Rai: To fly or not to fly: best way to travel from Chiang Mai to Hanoi?
Quickest and best is fly to Bangkok then onto Hanoi. Overland eats up time and is arduous.
AVietnam: 3 Weeks itinerary/Must sees for Vietnam/Cambodia?
It depends on time of year and weather patterns but Hanoi /Halong Bay Vietnam would take a few days. Plan for a week minimum if you want to include Sa Pa. Another few days Hue is a must see...
AVietnam: Best itinerary for two weeks in Vietnam? We want to start in Hanoi and finish in Saigon/HCM or vice versa.
Book the train. You will need separate tickets for each leg of your journey. Sleeping on the train allows you to see more and save on hotel bills. It's great way to see the countryside.