Before finally settling in to live in Thailand two years ago, I did my homework and visited every SE Asian Country. Except for Saigon, which was a mess, I liked VietNam a lot, especially the beach town at Nha Trang and the nearby mountain villages around Dalat. Cambodia very beautiful, very cheap. Myanmar poor and a little scary, Lao too chaotic for my tastes. Thailand won hands down. Best infrastructure, best food, most welcoming atmosphere, most variety of landscape.
I think I'd like to visit Indonesia the most
Difficult one... In overall I'd say Thailand, but the Philippines is getting more and more interesting the more I get to know that amazing country.
My country Vietnam is the best for me.
Burma/Myanmar for off the beaten track. Not much of a clubbing scene but you can get Guinness in a gay bar in Rangoon.
many people like Thailand but I don't know the reason why
In no particular order, Indonesia, Thailand, Myanmar, Laos, Cambodia, Vietnam, South Korea & Japan.