Best way to get from Chaing Mai to Koh Samui

Is this enough time?

I think so. It depends on you really, I mean they're beach destinations, so you can allocate as much time for lazing on the beach, swimming or snorkling as you can handle. There's not much of interest culturally or historically of course so it's not like there's any kind of list of things that you'd need to cover.

What would be the best way to travel between? In terms of time and Cost?

Cheapest (air) : Fly Air Asia CNX-BKK and then BKK-Surat Thani, then ferry
Most convenient : Fly Bangkok Airways direct CNX to Samui.

Or combinations thereof.

Cheers,
Chanchao

I just wrote out a long reply and my internet connection went down when I posted it. I hate it when that happens.

Anyway, I was saying that although the Chiang Mai - Ko Samui direct flight is relatively expensive (c. 7000 baht one way), it does save a lot of hassle. Given your relative lack of time, it is well worth considering swallowing the high cost and taking this flight. Bangkok Airways is a very pleasant airline to fly with, too.

Another way that I tried recently was taking an overnight train from Chiang Mai to Bangkok. On arrival in Bangkok, I took a taxi straight to the airport, and caught the Air Asia flight to Surat Thani (most of the time you will be fine doing this, but bear in mind that train delays can occur, although if you get the first overnight train from Chiang Mai your train would have to be very delayed indeed for you to miss your flight).

The main disadvantage to this way of doing things is that Surat Thani airport is a long way from Don Sak pier (where boats to Ko Pha Ngan and Ko Samui depart). Once your flight touches down at Surat Thani airport, it's the best part of 2 hours on the bus to the pier. Then you'll probably have to wait for a ferry, and then it's 3 hours on the boat to Ko Pha Ngan (Ko Samui is a little closer).

As Chanchao points out, you can also Air Asia it from Chiang Mai to Bangkok, then take another Air Asia flight to Surat Thani. But then you've got the hassle of changing flights in Bangkok (and as Air Asia is a point to point airline, they don't check your luggage all the way through to Surat). And once you get to Surat Thani, it's minimum 5 hours to Ko Pha Ngan from there. Overall, although the direct flight is more expensive overall, it does save a lot of time and hassle, particularly given your relatively short holiday.

There's only one daily direct flight Chiang Mai - Samui and yes it's fairly expensive and is often booked well in advance. But with your short timeframe if you don't mind and you can get a booking I'd say fly direct to Samui, hop to Ko Phangan after a couple days (or transfer directly since the Samui airport is very close to the Big Buddha pier to Phangan which IMO is a better island). Then do the connecting Lomprayah ferry/bus back to Bangkok.

Fly. You can take the train to Bangkok, a bus and boat to Koh Samui. Long trip. Very tiring, lots of hours. Fly it is simple, and you will feel like doing something when you arrive. On Samui be sure and visit the 3 Monkeys restaurant, free wireless and aircon upstairs.

Fly direct if money is not your main concern. Bangkok is Asia's award wining boutique airline. Great service and free coffee, tea, juices, and internet (CNX) at Chiang Mai and Samui. I remember leaving Chiang Mai about 10:30am and was at the hotel then on the beach by 12:30!!