Best ISP in Sydney

Hey guys, I'm currently in Sydney and I have a plan with Optus. 500 GB and 100 megabits per second download. They claim to offer us 100 megabits but in reality we only get 30-50 ish and this week is not the first time it has went down to 3 megabits per second. We are thinking of changing as we are not getting what we are even paying. Any tips on what to do? Also what other ISP's do you guys recommend and what plans are you guys on.

Cheers!