So its always advisable to purchase modems that are supported by your ISP.(Note: This is applicable to only those people who are not well versed on how to setup their modem) If your service provider is Optus then you can buy the following modem.
List of ADSL2 Modems Supported by Optus
Netgear N600 ( Recommended)
Basically all Netgear modems are supported by Optus but its always recommended to buy the one that your ISP suggests.But it all depends on you dear people. If you think you can setup a Cisco or Belkin or D Link then go for it.
If you face any problems setting up your modem, Please don’t hesitate , contact me right away and i will surely assist.