I normally use Standard Chartered American Express because they have the best rewards points system. Unfortunately, they have discreetly modified their rewards scheme so they are no longer the best credit card in Hong Kong.
The best card is currently the DBS Black American Express
HK$6 = 1 air mile
followed by the Citibank PremierMiles Visa
HK$8 = 1 air mile
For the air miles rewards scheme, it is better to enrol in Krisflyer than Asiamiles because you need less points under Krisflyer to get an air ticket to Singapore. I think it is 22,500 for Krisflyer compared to 30,000 for Asiamiles.