I've never really heard of rankings for primary schools but a google brings up some references that may be worth looking at: Sydney Primary School Rankings - Google Search

You might want to look at where you plan on living as well for prices of real estate rental and buying will vary significantly from established suburbs closer to coast to those out west and southwest in particular.
www.domain.com.au will give you an idea on pricing and the rule of thumb can be the lower priced newer suburban areas could have public schools which have less of the community/parent support that comes with time.