How set are you on a biomedical pathway?
If you're not sure about doing med, I would go for the bachelor degree in science or biomed. It gives you a lot of chance to build skills in general biomedical science, opening up pathways into medical research (before or after you do a medical degree - you can always go back!) and building a lot of good foundations which you don't get going straight into an MBBS. If you're set on some sort of biomedical field (but are not sure which health science profession/medical research), I would be tempted to recommend Biomed to you. I personally have found the standards of teaching in our course to be very high, and I personally find the large amount of diversity to be a plus.
But if you're set on medicine (most likely in the clinical sense), I would go for an MBBS course - considering interstate as well as Monash. As others have indicated, you need to back yourself pretty heavily to get a decent GPA, GAMSAT and then interview - ENTER isn't tooo great an indicator of how you will go in these areas. I know people with quite good ENTERs who don't do so well at uni and are worried about their potential to get into med atm (and of course the other way round too). It's worth noting that the ENTER to get into biomed in the first place is pretty high (and a lot of these people are competing for med)!