ANU FTWUnless you have attended every university within the Sydney region no one can really say which uni is the most 'prestigious' or otherwise you're just speaking for yourself from a subjective viewpoint.
However ANU, the Australian National University in Canberra is considered the most globally recognised in terms of its intensive research based degrees and high quality of professors i.e. there are apparently 6 alumni and staff that are Nobel laureates which could account to your so called 'prestige' factor.
Personally just go to whatever uni cause in the end the one what works the hardest and has lady luck on their side ends up making the dollars.
on the point of Nobel laureates, one of the winners of the nobel prize in physics in 2011 is a current ANU professor.