How to maximise point earn by using credit card for business expenses?

I’m new to all this points/ travel space, we can now pay our suppliers monthly $250k+ with little or no fees for CC purchases.
So I need to work out which is the best bank for that.
I might be able to use Amex for some and a reduced fee, so that could be an option.
After reading a lot on this site, i’m even considering 2 cards 1 Amex, 1 Visa / MC, does use that option currently?
We currently bank with ANZ and they are suggesting their Black card.

Appreciate any suggestions, cheers.