The math is simple enough that it almost feels like cheating. An overnight bus from Chiang Mai to Bangkok costs roughly 600–900 Thai baht depending on the class. A decent budget guesthouse in either city runs 400–700 baht a night. You are, in effect, paying the same amount to sleep and travel 700km rather than paying to sleep and go nowhere. Do this four or five times across a longer trip and you’ve essentially funded an extra week.
This isn’t a secret - backpackers have known it for decades - but most travellers now default to budget flights without checking whether the overnight bus actually makes more sense. On routes where the flight is two hours but the airport transfer, check-in, and wait add three more, a nine-hour sleeper bus starts looking rational.
The class difference matters more than the operator
In Thailand, Vietnam, and Malaysia in particular, the gap between standard and VIP overnight buses is significant enough to change whether you arrive functional or destroyed. Standard buses have reclining seats. VIP buses - sometimes called “sleeper buses” - have individual flat or near-flat pods, usually in a 2-1 configuration, with a blanket and sometimes a small meal included. The price difference is often 150–300 baht, which is nothing. Always book the better class.
Vietnam’s sleeper buses (the ones running the coast between Hanoi, Hue, Da Nang, and Ho Chi Minh City) have become notorious for their coffin-bunk layout, which is either charming or miserable depending on your height and claustrophobia levels. Anyone over about 180cm will have their feet pressing against the partition. This is a known, consistent fact about these buses - not a one-off complaint.
One real warning
Station arrival times are usually 4–6am, which means you reach a city before most accommodation will check you in. Budget for this. A cheap café, a bag storage service, or a morning walk absorbs the gap better than sitting in a bus terminal. This is the actual hidden cost that makes people swear off overnight buses - not the sleep, but the two hours of limbo at the other end.
Book through 12Go or directly at bus stations. The latter is usually cheaper, occasionally chaotic, and almost always fine.