Ok, well I'm one of those people that had Monash as my first preference and didn't get accepted. But I did get into UMelb, lol.
Um, because UMelb is like, the 2nd oldest university in Australia (after USyd, I think) and their med school is the oldest (I *think*) in the country, it is considered to be more 'established' and prestigious. UMelb is also affiliated with a 'prestigious' teaching hospital - the Royal Melbourne Hospital. If you did a street survey, most people *would* consider UMelb to be more 'prestigious' than Monash. But whether the prestige of what med school you attend actually has any impact on your career after graduation is very questionable.