I'm not in Australia (far from it), but I have a friend who lives in Maryborough, Victoria so I iMessaged him (he has an iPhone). He says Telstra is the best.
Hate to say it as a Vodafone customer, but if you NEED the speed, go with Telstra. You will pay through the nose for it though. Check the maps on their site for coverage and types of service of your area.