If you got into PhB, you'll pretty much certainly get a place at Monash. If you'd much rather study law, go to Monash, by all means.
Unfortunately, I do think that the benefits of living in a residential college outweigh the cons. I've lived both at ANU and at Yale, and both are very different schools. However, living in a college gives you a chance to make a lot of new friends, whereas at commuter campuses such as Monash, people try to squeeze all of their classes into as little time as possible so that they can go home. That means that a lot of people stick with their high school friends. Another plus of living in a college is that it's so much easier to do extra curricular activities or study groups.
I do miss living at home though - I miss my family and having more personal space and stuff.