Done the return leg Samui BKK last June by train.
Not a bad trip as it goes,we got the first class sleeper which from memory was around 1400 Bht bought in Samui.
This included pickup from hotel on samui, ferry to mainland,coach to surat thani train station,sleeper to BKK.
The first class sleeper is by far the safest as only first class passengers are allowed in the first class carriages and the carriage in front has a police officer present.
The steward shows you a menu to order drinks and meals which he brings to your carriage and makes up the bed for you at night,wakes you up with breakfast in the morning and turns the beds back to seats.
There is a small sink and taps where you can brush your teeth in the corner of your carriage. The toilets in first class are clean and also have a shower.
Only problem is,if you want to mix with other travelers you cant do it in first class because you have no access to the second class carriage.
Go to youtube and have a look,there are a few clips of the first class sleeper.
next time I head that way it will be by coach/ferry combo ticket,quite a bit cheaper as well.
www.seatran ferries have a map of the route, BKK to Hou Hin by coach,Hou Hin to Chumphon pier by coach,ferry from Chumphon pier to Samui via Koh Tao and Koh Phangan.
Lomprayah fast ferries also do this trip.
The thing I like about the coach/ferry is you can stop off at Koh tao and then Koh Phangan for as long as you like with the same ticket.
I also like this route because I didnt like samui and have no intention of returning,so I would stop at phangan.
A lot of people look at the map and think Surat Thani (where you get off the train or plane) is just up the road a bit from samui! It can take quite a few hours to get to Samui from Surat Thani.
By far the best way is to fly to Samui from BKK.
bangkokair have some cheaper flights late night or early morning.
Flying to Surathani airport is a lot cheaper but a false economy when you consider getting from Surat Thani airport to Samui and the time it takes.
Sleeper train is great if you are sick of flying as we were. :)