IMHO anyone in this game should have an Amex Plat Edge in addition to at least one other card.
The free rtn dom flight that comes with Plat Edge each year more than negates the annual fee, and almost everyone spends a fair bit at supermarkets, so why would you not use the Plat Edge to earn 3 pts per $? It also has some good bonus point offers.
For everything else where Amex is accepted (within Oz), Altitude Black Amex is my go to card, for 1.5 pts per $. Where Amex is not accepted, I use Citi Signature for 1 pt per $, and similarly I use Citi Signature overseas (2.67 pts per $).