One of the first decisions you’d have to make is whether you want to earn ‘flexible’ points or lock yourself into Qantas Points. It seems you have already considered factors like annual fees and points earn rates. But the main thing is, do you see yourself using Qantas points primarily or would you like the flexibility that something like the altitude points program provides in being able to transfer to Virgin Velocity, Asia Miles or Krisflyer.
Another point to consider is that the AMEX card might not be suitable for all business owners depending on if the expenses your business currently has can be paid with AMEX. The Westpac cards are more versatile with their Mastercard networks which basically everyone accepts whilst that’s not always the case with AMEX. Of course, choosing Westpac cards means sacrificing on some points earn if you are looking for Qantas points.