Advanced Booking Needed on Overnight Bus/Trains from Bangkok to Chiang Mai?

Having tried both, I'd opt for 2nd class as being a better sleep ( bunks are lengthways as opposed to crossways in first ). Also, Thai first is not same as a western first- no ensuite bathroom.
However, OTY and as #19 says if you are on your own, you may have to share with a stranger.

I agree with TBL, 2nd class is the best for the trip. I always had a good sleep.

^^ Likewise, I always sleep well in lower bunk, second class AC carriage.

You should be able to get a 2nd class or 1st class berth on the Wednesday but you could be unlucky so it really depends on how important it is to travel on the saturday and not either the Friday or Sunday

Thanks much, good stuff. Going with wife so if I don't screw up too much should be comfortable enough. Nice to hear the 2nd class sounds perfectly comfortable as well. I am thinking will opt for an earlier buy as we are fairly loose but do have some res up at Chaing Dao Malees.

when i arrived in bangkok yesterday, i headed to hua lamphong to buy a ticket a day early to be safe. to my horror, all of the afternoon trains were completely sold out. the only tickets available were 2nd class no air con for a 12:45 train that gets into chiang mai 04:15. i.e. almost booked out a day in advance. i got them to check the following day - the same too.

checking the current day (even though i knew i wouldn't travel on it), there were strangely 50 tickets in each class (i.e. loads). with more probing i was told that if i turned up the following day and checked at 10am, there will likely be tickets, because people can change them.

yesterday i got a 12:45 ticket as insurance (bad train, i'd lose time, but gets me to where i want at a decent time) and this morning i turned up and there were tickets available for the 18:10 train (i.e. the good one). i got second class, lower berth, with air con. exchange fee was 50 THB and i had to make up the difference in cost.

so, the 10am "exchange" is quite important. that seems like the best time to get a ticket.