From an internet cafe in Chiang Khong...
Thanks to the advice from few different internet message boards, we went to the Chiang Mai Arcade Bus Station yesterday to book our bus ticket on the Green Bus company for the 8:30 service to Chiang Khong. It seems a lot of people start booking this route 1-2 days in advance (I'd been tracking the number of seats sold online), so it's best to book early especially if you have a few people traveling with you, want to sit together and/or don't want to sit in the very back.
The bus itself was older than the ones I had taken in Argentina, Brazil, and Turkey, but the seats offered pretty good legroom. A pleasant surprise was that there was an attendant on board who served bottled water, snacks, and wet naps. This rendered the late night run to 7-11 for snacks a bit redundant. For a few hours in the middle there was Thai sitcom playing on a TV in the front.
We made three 5-15 minute pit stops at bus stations en route, where you could use the restroom or buy some snacks. Total trip time was 6.5 hours, and you are dropped off at the bus station in Chiang Khong where there are a lot of tuk tuks waiting to transfer people. I'd read online that a lot of the shuttles organized by guesthouses in Chiang Mai and in other cities drop you off at a pre-selected guesthouse late at night, since they make their income through the commissions. Taking the Green Bus company is a good way to avoid this.
