The question is simple but the answer requires careful consideration. There are so many cities in China it is hard to say. Then I don't expect that many people have seen all China. I certainly haven't. But judging from what I read and hear, the truly interesting cities are : Shanghai, Suzhou, Hangzhou, Nanjing, Wuhan, Hong Kong, Guangzhou, Shenzhen, Guilin, Kunming, Chongqing, Chengdu, Xi'an, Harbin, Ürümqi, Lhasa, Taipei and Beijing.