Jetstar is owned by QANTAS and are serving in Airbus fleets. Virgin Blue is owned by Virgin Groups. They are using Boeing fleets. They are similar with the budget airlines, you need to make your booking online and the price is varying. I like to use webjet.com.au. It can gather the price form both airlines. Then you can compare to use the cheapest one. But there are a few things you have to be aware to use budget airlines. Firstly, the airplane you choose to use. Sometime, they will land the airplane away from the city. Moreover, luggage charge are not included with air fare normally.