I work at dick smith part time, so i can tell u that if you want any type of decent connection you will have to fork out money for the bigpond one. It has the coverage the others don't. But you can check on all of the brand's webpages for availability of coverage by typing in the address you will be staying at.
There are two telstra wireless modems, the 7.2mbps and the everyday one. the 7.2 is only available at telstra shops or T-life stores i beleive. it is more expensive initially but has better coverage and faster speeds.
hope this helps a bit, i know telstra is awfully expensive, but it would be tax deductable on the upside