Telstra the coverage is still better even for those NSMen and NSF that is going to Exercise Wallaby or other NS Australia Exercise..
Those area hardly can even receive any optus or Vodafone signal.
Telstra wise will usually be more expensive. If you don need a card straight away from disembark from the airport. I would suggest heading to the supermarket like Coles and Woolworth to buy the card. The only diff is that you need to find a wifi spot to register after u purchase the card or u can walk into any Telstra or Optus official store to seek their help to help you activate the SIM Card.
A lot of saving can be got from the SIM Cards that is purchase through the Supermarket. Check out those bigger branch. The SIM card are usually located near the aisle of the cashier or near the part where the cigarette is purchased.
Those getting it or not sure of anything regarding coverage or SIM card stuff can post your enquiry and I will get back to share with you