My money is also on the Max.
The group wide economies of scale (regarding the bus) will be negated by Airbus being able to bend Qantas over the barrell with any fleet planning in the long distant future should all (but a few 787s) already be operated by that one manufacturer. Divide and conquer works beyond the pilot group.
Mostly however I say Max because surely they must be cheap which seems to be the priority in local fleet acquisition.
For that reason I also can't see A220s coming. Ever.