The train (with sleeper bunk) was very comfortable in my opinion. I was going from BKK-SIN so I don't remember how long it took but it didn't seem 'long' or really boring at any time... I guess my judgment may be a bit colored since I had just finished a few days of traveling by van through Vietnam and Laos, and had taken the trans-siberian a few months beforehand If you're flying economy, opt for the train instead ^