I took the night train from Ayutthaya to Chiang Mai. For about 850 Baht for a sleeper car, it was quite a good experience. Despite the train being an hour and a half late, and stopping randomly for an hour on the track, all was well. But apparently, the train authorities have a very clear, cohesive message regarding timeliness of the trains:
I would certainly recommend the night train over the bus or flying. Travel time is about 13 hours, assuming the train arrives on time and doesn’t hang out on the track. But the cabins are comfortable and it’s not like being on the bus; the train rocks you to sleep quite nicely. In the sleeping cars, you will also have access to electrical outlets. Be sure to bring your adapters, though.
You get to see a lot of the landscape of Northern Thailand as the sun rises and it can be quite a social experience, especially in the dining car. I have read a ton of stuff saying book ahead. I booked the day of without any problem on a weekend during high season. So, if you dont book ahead, it is not the end of the world. If you are traveling with a group though, that might be the best option to ensure you are situated near each other. Most train tickets have “meal included” written on them. I found this to not be true. So, watch out for the train folks who walk around and hand you plates of food, seemingly for free. They come back looking for money…way too much money. Just give them a good assertive no and they will keep it moving. If you do get food or beer from them, keep up with what you’ve ordered. A few people were upset that they were being asked to pay insanely high prices or pay fro things things they did not order. Sketchy. But, certainly not a deterrent to taking this great journey! And of course, you can always bring your own snacks. If you get on in Bangkok there are plenty of places to grab stuff. If you hop on at Ayutthaya, there are snacks in the train station (which is really on outdoor platform) or at food stalls right across the street. If you are taking the sleeper car from Ayutthaya brace yourself for boarding, literally. The first step was about chest height for me and the conductor literally was pulling people onto the train. I think my shoulder is still dislocated :).