eh they're the same, when I say same, I don't mean for every lecturer at Monash there is a similar one at uom or for every unit at monash there is an exact replica at uom, what I mean is both unis have about the same job prospects after undergrad, the comm course in both unis are very similar, and so on.
But it is extremely hard to compare the ENTIRE commerce degree b/w the 2 unis, you need to get more specific, ie what majors are you looking at? Say you're doing actuarial, then yes uom would be more beneficial than monash if you're not considering double degree. If say finance, then both unis are EXTREMELY similar in that regard, many of the professors teaching finance at uom have also taught at monash and vice versa, both unis also collaborate in research projects etc.
However if you are looking at postgrad, you would definitely want to do it at uom, there are many reasons for this which i won't bother getting into as it is major-specific.