Hangzhou is indeed one of my favorite cities in China, in part because it is so much cleaner than everywhere around it... doubly impressive in light of the amount of heavy industry on the Delta.

But, I would also like to point out that there are lots of clean and pleasant places in China,... it just so happens that the vast majority of the places tourists and business travelers visit are tend to be filthy.

Anyway, if you want clean, check out Fujian near the sea or go west (Yunnan, Sichuan, Xinjiang, Tibet).