Whichever one offers you the job in the first place of course, then the basing you want, then balancing progression opportunities against eba provisions/pay that suits you.
You won't get all of that anywhere so weigh up whats important to you.
You don't necessarily need a jet job to get those either.
People will split hairs over the differences or cherry pick scenarios to make one operator or another seem better, but aide from basings and progression just about every mainstream jet operator in oz is as good/bad as the next in the big scheme of things.