In the end it all really comes down to comfort/practicality/personal style.
Messenger bags hurt the shoulder, so don't stuff them too much.
Last year alot of people at usyd (guys and gals) were carrying those country road duffel style bags.
The girls all like oversized handbags. I suggest Sportsgirl, Equip, Glassons etc for some student budget friendly finds. Some of them go simple with a "supre" type bag.
The guys either have a backpack/messenger bag... or nothing at all.
Hope that helps...
In the end try not to stress so much about the bag... everything falls into place eventually ... trust me.