I hold a HSBC Premier Mastercard, a CitiPremier Miles Visa, and a CX Amex. The Amex and Citi both give 1AM/$8 for local spending as the base position. The HSBC is 1AM/$15. My spending tends to get spread around depending on the promos in place.

At the moment HSBC is offering me a $1/38 cash-back on spending at major HK retail outlets (Wellcome/PnS/Mannings/etc) so that's where those go just because 2.5% cash back is better than any miles deal. Everything else is going to Citi because they have a targetted promo at the moment which offers me slightly better miles on a tiered basis depending on a personalised spending target, but even without that it would be my default card because there is no expiry on the miles whereas the Amex transfers automatically and hence immediately goes into the AM 3-year expiry. The exception to that is in the case of travel or major purchases where I value the insurance then I try to use the Amex if possible. The Amex remains free because I am CX Silver. The other exceptions are where the card offers a significant discount in dining or other establishments - then that card gets used regardless of the miles impact.