If you're at a large US airline, I'd stay put. There are likely to be much better days ahead in the US as all the baby boomers start retiring.
I'm not KA, but they fly some pretty tired airplanes in Chinese airspace that is far from relaxing. The upside is all the day flying, but I think it would be quite fatiguing nonetheless due to multiple sectors in China.
The Chinese pollution is ridiculous, and the cost of living is outrageous in Hong Kong. Not just housing, everything is expensive in HKG except taxi cab rides and fake Rolex watches.
I cannot imagine your quality of life will improve at KA on the current package unless you are a dirt poor regional pilot in the US. Even at that, your salary will have to more than double coming to KA just to maintain your current qol in HKG. If you love the big city, go for it, but it is probably not a career move.