I can only vouch for Thailand. I loved the place. Spent time in Bangkok, Chiang Mai, Phuket, Koh Phi Phi, Koh Samui and Koh Phangnan.
Bangkok is a very intriguing experience, you'll be able to get a real taste of Thailand there.
I did a trek in Chiang Mai and thought it was great you can visit the Kayan tribe (women with elongated necks) numerous waterfalls, see the tropical forest etc
Koh Phi Phi (both islands) are beautiful and you can't help but relax there.
Samui and Phangnan are ok. More so party islands, although there are some really nice attractions there too.
That was a brief summary i can go into much further detail if you like the idea of any of those above. Give me a shout if you need help.