Thailand forum

In March the weather on both sides is still ok -- the weather on the Phi Phi side doesn't start really deteriorating till April/May.

Transport-wise, it depends on how much time you have, as with the low cost carriers the airfares are not all that much more expensive than the train/bus.

If you can set a date now for when you want to fly from Chiang Mai have a look at www.airasia.com - we used them in Thailand and Cambodia and they were great. At the moment they have tickets for as little as 399 baht + taxes all over Thailand... you are looking at about 1000 baht for a ticket from Chiang Mai to the Islands area!

Ike, I think better option for you is use regular ferry.
You can see schedule:
http://www.thailandday.com/Boattransfer/kophangan.html
So, for day trip you can start from Samui at 09:00 and return back with 16:00 Songserm Express.

Sofia, there is no direct buses between Singapore and Pattaya.
You need to take bus from Singapore to Kuala Lumpur, than change bus to Bangkok (or possible to Butterworth, then to Bangkok). And at last take bus to Pattaya from Ekkamai bus station in Bangkok.
By the way, do you know that Kuala Lumpur - Bangkok is a 21-hours journey? Are you ready for this? :)
I suggest to take train because it is more comfortable and not so expensive.

Schedules, information:
http://www.cuti.com.my/guide/plusliner_fare.htm
http://www.journeymalaysia.com/ptasingapore.htm
http://www.the-inncrowd.com/singtomsia.htm#kl
http://www.transport.co.th/Eng/EAST1.htm
http://www.railway.co.th/english/images/south.gif

Sofia, there are no direct train between KL and Pattaya too :)
First, you need to take train from Singapore to KL, than change train to Butterworth, then again change thrain to Bangkok.
You will arrive from Butterworth to Bangkok. Then go to Ekkamai bus station and take bus to Pattaya (information above).

Singapore - KL ~ 7h 30min
KL - Butterworth ~ 9h
Butterworth - Bangkok ~ 22h
Bangkok - Pattaya (by bus) ~ 2h 30min

See booking information and schedule:
http://www.seat61.com/Malaysia.htm

According schedule, if you start from Singapore at 13:00, change train in KL at 21:00, in Butterworth (06:05 - 13:15), then you will arrive to Bangkok at 10:50. Total time is ~ 46h Plus 2h to Pattaya :)

By the way, train ticket Butterworth-Bangkok costs ~1200 thai bahts ($37). But fly from KL to Bangkok on AirAsia (see http://www.airasia.com) will cost you 140.99 malaysian ringgits ($41). Direct AirAsia fly from Singapore to Bangkok (~3h) will cost 77.99 SGD ($51). So thing about time, when make decision :)
You can book AirAsia at their web site (link above).

Ah! There is direct bus to Pattaya from Bangkok international airport :)