Fastest - fly from Bangkok to Koh Samui.. I flew Thai airways for about $100 USD. Bangkok airways also flies that route.
Cheapest - bus or train to Chumpon then catch the ferry to Koh Samui.
Travelfish have some good info, including some things to watch out for here: http://www.travelfish.org/feature/57
PS: My favorite island was Koh Tao by far! Way more relaxed and beautiful.
Have fun! almost 10 years ago
Flying to Samui is expensive compared to other domestic flights in Thailand because Bangkok Airways own Samui airport and therefore restrict the carriers that can land there. Air Asia, for example cannot.
I suggest taking the sleeper train from Hualamphong Station (pronounced Wah-lom-pong) down to Surat-Thani and the ferry from there. When you buy your ticket at Hualamphong you buy the full journey which includes train, short bus ride to the port, and the boat.
The trains leave Bangkok at about 7.30pm and you should arrive in Samui at around 9.30the following morning. A 1st class cabin will cost you about 1,300 baht, but we onky ever did this once... we find a 2nd class cabin with a fan is much more fun and only about 650 baht :-) You can discuss all ticket options at the station.
One word of advice is that if you are here in high season and heading down to Samui / Koh Phangan for full moon or new year then go to the station and buy your tickets as far in advance as you can, as they get booked up very quickly. If you find the sleeper train is full you will most probably be offered a bus instead.
The bus isn't too bad, the seats recline quite a way and they give you blankets etc, but the train is a much better option.
Here are some train times etc - http://www.seat61.com/Thailand.htm#Ko%20Samui
Have a great time! :-) almost 10 years ago