It wasn't on your list, but I'd probably chose Japan. A friend of mine taught there.
My sister-in-law taught in South Korea. She had good experiences but I would feel too uncomfortable about the way women are treated (I don't know the details, and part of it might have just been because she was a foreigner, but it didn't sound pleasant).
Out of your list I chose Thailand, but I would prefer Indonesia. I think its just a much more laid back country. The others all have pretty strict laws and not so modern ideals. Bahasa Indonesia is relatively easy to learn to speak and read as well.