I did Bachelor of Science (Statistics) at RMIT for a year before transferring to Melbourne Uni.
At RMIT, you get very little choice in terms of what subjects you do. Most of your degree is structured for you. At Melbourne, you get a lot more choices and they make you do more breadth subjects.
At RMIT, they force everyone to do Calculus 1. Even if you got a 50 in VCE specialist maths, they'll still make you do Calc 1. At Melbourne, they let you skip to Calculus 2 if you got a 27+ in spesh and Accelerated Maths 1 if you got a 38+ in spesh, so there's a lot more freedom for a stronger maths student who wants to skip ahead.
The assessments are easier at RMIT. For example, the exams tend to go for 2 hours at RMIT compared to 3 hours at Melbourne. Also, the exams are usually only worth 50-60% at RMIT (some subjects don't even have exams), whereas Melbourne exams tend to be worth 70-80%, which makes it much more difficult and stressful.
Also, the assessment at RMIT isn't treated that seriously. For example, in Calculus 2 at RMIT, we had 10 weekly tests worth 4% each and an exam worth 60%. In the weekly tests, you were allowed and even encouraged to "discuss answers" with other classmates and the tutors would walk around helping people. So basically everyone shared answers. It was ridiculous - an easy 40% for anyone who showed up to class and copied answers off other people. At Melbourne Uni, the tutors take tests much more seriously. You really need to earn your marks at Melbourne Uni.
The average lecturer seems to be much better at Melbourne Uni compared to the average lecturer at RMIT, plus the facilities are so much better and the campus is so much more amazing (some of the buildings at RMIT, particularly the engineering buildings, look like they need to be demolished).
If you're planning on doing maths or statistics, I would choose Melbourne Uni over RMIT in a heartbeat.