Mine:
Foreign spending - SCB AE ($2.5/mile), followed by HSBC Platinum Visa for non AE merchants ($2.78/mile).
Travel agents - SCB AE ($2.5/mile)
Dining & AAVS - Shacomm Platinum Visa ($4/mile and $8/mile respectively)
Bills Payment and CUP local as well as overseas merchants (over HK$300, till end of 2011) - BankComm Diamond CUP (HK$4/mile). They do have a current promo of 3x Bonus Points for Welcome Offers (up to HK$18,000). That translates to HK$1.6/mile (correct me if I am wrong).
Other Local spending - DBS Black Card (HK$6/mile) followed by Citibank PM (HK$8/mile) for non AE merchants.
Supermarkets - my wife usually does all the shopping and she uses cash most of the time. If there's some promo with the Wellcome located downstairs, I would go with Citibank PM ($8/mile) as they give some cash back (like the current HK$75 for spending HK$500). I got HK$60 for a one-time spending of HK$500 in July.