Shanghai is the prolly the wealthiest, cleanest, most modernized and westernized city in China. Its European influence goes back a century when the British occupied it and built the Bund (the coastal strand of western architecture). There are some really nice closed-off shop-lined streets to shop around and get bites to eat. Lots of new money and rapid growth - one might say the new face of China... Accordingly, "Shanghai girls"are often pretty but notoriously stuck-up and snotty. And, Yao Ming also played for the Shanghai Sharks hoop team there!
I was last there in 2000, and if you're looking for a modernized Chinese city - it's a far cleaner and preferred alternative to HK for me. However, if you want a more traditional old-style Chinese town, obviously neither is your bet!