We're located in Bangkok and I can really recommend it. I've not been to Chiang Mai so I cannot really compare it, though I would guess Bangkok is still more startup friendly.
To address the current political issue with the military coup, I have just one thing to say: The media always exaggerates. I've been here through the protests, the curfew and now the coup. And I've never felt threatened or had any issues what so ever. I would invite my own mother here and not be worried.
We are currently sitting together with another startup in their offices in the part of Bangkok called Ekkamai. Previously we rented some desks at the co-working space Launchpad, which was also a really great experience and a way to meet a lot of other like-minded people.