Is Coinspot.
Trust me I have tried them all. They have the best rates, they have the highest credit card buys(up to $5000 per 24hr) and instant bank transfers via POLI.
Other sites either have worse rates, or limits on credit cards Coinbase.
UPDATE Coinspot have removed credit card purchases.
Coinjar is quite good too although their rates for buying aren't as good.
After buying their EFTPOS card I would advise against it. You can withdraw bitcoin from Coinjar very easily to your bank account. It is easier to just use your own bank account.
Localbitcoins also don't have as competitive rates and is more trouble than doing it all online.
I highly recommend Coinspot if you want to buy bitcoin in Australia