I realise I didn't really answer the question. From my experience, Guangdong is a pretty great place to retire. I have a soft spot for Hunan, as my wife is from there, the spicy food is great, the landscape is amazing, the climate is pretty good and it is only 3 hours high-speed train away from Hong Kong and Shenzhen. I would go for 2nd tier cities, like Changsha, Willy's beloved Zhongshan, or Zhuhai as the megacities are too expensive and too hectic and polluted (I think) for a good retirement life. If you are adventurous, you could strike out in far-flung places like Xinjiang (where my step-daughter works) or Yundong, which has that sub-tropical climate, or Sichuan/Chongqing with spice and natural wonders. For those places, you may need your Mandarin to be OK, unless your wife can handle all the talking.
Let me know if you want any more details about living in China or specifics about Hunan, Guangdong, Chongqing, Chengdu, or Shanghai as I know about those places. Visas, bureaucracy, bribery, food, shopping, accommodation, work, hospitals, driving, travel, natural and cultural sights, growing stuff, family politics, etc. Just ask, I may be able to help.