My feeling for this bird is that it is a female Hainan Blue. I agree with Brendan that these are clearly very similar species, and separating them is likely to be very difficult based on current knowledge. Hainan Blue is a fairly common breeding species, whereas Blue-throated is still very rare, so Hainan should be the expected species.
Although the breast on the second image here looks fairly well defined, I think that is partly related to the angle of the bird. On image 1 it seems more diffuse, and similar in colour to the upperparts. This feature is more expected on Hainan Blue than Blue-throated (I think), also the eye-ring seems relatively narrow and poorly-defined. Overall I favour an ID of Hainan Blue for this bird.
