When I lived there it was luck of the draw.
-The downtown public hospital (Chiangrai Hospital) helped me a few times, long wait but satisfied, they had my medicine which I couldn't find in the other hospitals, can't beat the rates they charge.
-Sriburin: precancerous lesion got misdiagnosed as allergies by a very pompous dermatologist.
-Overbrook mostly ok, but not level of Chiangmai hospitals; when I needed a scan they sent me to the provincial public hospital.
I think the suggestion of MFL, and generally checking individual doctors, is good.