HKG? You want us to move to an airport?

Funning aside, HK air isn't all that great, too much imported pollution from the Pearl River Delta. The only larger Chinese cities that I've been in that seem to have decent air are Dalian, Qingdao, and Xiamen. Xiamen I particularly like since in ways it reminds me of my original home (coastal Florida) and doesn't have a real winter. Inland: Kunming has pretty decent air. So, Xiamen or Kunming would be my picks, and maybe not just based on health/air quality but on general liveability dimensions and easy access to places outside China. Shanghai I could deal with but I'd put a time limit of 2 years on it.