Rankings are so dodgy i wouldn't even consider them as an undergrad.
The fact is this - All (pretty much) your professors and lecturers will have PhD's or be highly knowledgeable in the field. This is true no matter if you go to somewhere like ANU or Monash or La Trobe or RMIT. They're not total dropkicks, they're smart, knowledgeable people pretty much anywhere. It's not like the professors at ANU have some secret knowledge those at RMIT don't, especially for undergrad subjects which can be fairly broad and general.
To be honest as a student, rankings aren't the very first things you should be looking at. You dont take the whole university, you take a specific course. You should look at how that course is structured, if you're in something like law or commerce then you should consider how that course and uni are thought about by employees, you should look at oppertunities; At monash for example in one of the developmental biology subjects you can work in a stem cell laboratory for a period of time and Monash also offer subjects in your 3rd year that are like mini-honours. They're full year units and let you do a little research project. You should look at the kind of support the uni provides, the atmosphere, how close it is to where you live, clubs, ect. You have to be a whole lot more holistic.
The fact of the matter is, these things will have a much bigger impact on your day to day experience than rankings ever will.
The ranking methodologies are really dodgy as well. Hardly anyone knows what exactly they plug in and how. Researchers tried to recreate the shanghai jiaotong rankings, using the formulas and data the shanghai ranking people published. The idea is if you use their formulas and data, you should get the same rankings out of it as they did. The researches got something different. So, theres room to fiddle or have some other weird unknowns in there.
Rankings are obviously a pretty good marketing tool for uni's as well and they'll do what they can to boost their rankings without necessarily translating into something good for the average undergrad.
UoM/Monash/La Trobe/Deakin are all pretty decent universities. RMIT is very good and innovative in certain areas as well.