I'd still give a lot of thought to Melbourne. If you are the exact same candidate with the same development opportunities and the only difference is the university that you attended, I'd agree that the prestige difference is not very significant.
However, there are exclusive UoM development and growth programs that Monash does not offer, one specific one that made an enormous difference to me was the International Case Competition program. You go through 8-12 weeks of rigorous training after being selected through the summer holidays and you have the opportunity to work with some of the most intelligent and driven peers you'll ever meet. There are many more that you can read about on the UniMelb website.
Participating in the program was the biggest reason driving a lot of the internship/job interviews that I was able to secure in 2017 and would honestly say it's made a very tangible difference to my graduate salary (if this is a factor that matters).
That being said, if you're a top student, you'll excel anywhere. There are many, many phenomenal students from Monash and they definitely do end up in some of the most highly regarded graduate positions.