There are 2 main bus stations in Chiang Mai: Arcade - the main one east of the river towards the train station which tends to have the large blue air-con buses heading off for more distant destinations, though it also serves as the terminus for all stops in Mae Hong Son Province including Mae Sariang and Pai, and Chang Puak bus station serving all local destinations. I took a VIP bus from the Arcade bus station to Chiang Rai which left at 10.15am, took 3 hours and cost 280 baht. It was a lovely bus with reclining leather seats with leg-rests and miles of legroom and space, a/c and a piece of cake and bottle water thrown in for free. You'll pass by some lovely scenery on the way plus go over some big hills. I arrived in Chiang Rai at 1pm.