Use cash, it gvies you more flexibility and bargaining power. Just take AUD with you and exchange it on the fly. The local exchange booths are competitve and if you hare exchange some larger amount, you can always try to get a better rate.
Credit Cards are good for high end stores and hotels. If you are friend with locals (who you can trust), they can tell you which store/shop are safe to use CC.
All in all, use common sense when it comes to CC, if it doesn't feel right, don't use CC.
Enjoy Shanghai, it is fantastic/futuristic city with lots to offer!