Seeing as most of Australia's military, naval and air force are located in NSW and Victoria, along with almost all of Australia's ordinance production and strategic command and military intelligence, not to mention of half of the entire population of the country... I think they might have a slight advantage.

Of course, on the off chance that they utterly destroy each other (they wouldn't because NSW would almost certainly win due to naval and air superiority), then no one wins... because none of the other states have sufficient military resources to capture and hold territory. Western Australia has enough naval presence to capture ports but not enough boots on the ground to mount an invasion.

In any case, no states could effectively combat a guerilla force in Tasmanian terrain. It would just be our own version of Vietnam... but a bit more laid back.