Your ultimate aim is to work for a law firm I assume. You are increasing your guarantee by going to either Monash or Melbourne, indisputably the best law schools in Melbourne.
One point thats missing in this thread is in regards to marks. Its been noted that if you want to get into Melb law (say HD average and 155 or even 160+ LSAT) you need to work hard during your undergraduate degree to get HD. And theres no guarantee to get in. Thats true, but you are also hindering your chances of finding a job if you dont get D or HD average at Monash Law undergrad. So theres no realistic way that one can land a job without working hard, at either getting into Melb, or during your time at Monash. Point is, dont just go to Monash because it seems easier. There you will need to work equally as hard as trying to get into Melb. Both ways require D and HD average. For those who say experience > marks. Not entirely true. Good marks will more often than not land you interviews. From there, your expirience + good cv will finish it off.
What you could consider is. Doing an undergradute degree for the purpose of trying to get into Melb Law. However, if for some reason you stuff up your LSAT, theres always the chance of Monash JD. Theres no professional distinction between undergrad and postgrad law at Monash.
Its hard to get HDs at Melbourne, especially a course such as commerce. However, Melb JD considers all undergrad degrees on the same level. I know a guy who did a Bachelor of Education at Victoria and with a WAM of 90+ he was able to get into the Melb JD. Honestly, it is way easier to get a HD at Victoria Uni, especially doing arts based subjects than to get at least D in Bachelor of Commerce at Melb. Theres that.
Those are just some extra points.