As far as teaching quality goes, it is all subjective to you.
Some people find certain teaching styles more appealing than others, and there are heaps of lecturers with different teaching styles! So, you shouldn't really care about this as of now~
First of all, there is a difference between Monash and Melbourne's post graduate medicine entry scheme:
As far as i'm aware, Monash ranks its internal applicants based on their WAM and Melbourne ranks their internal and external applicants based on their GPA and GAMSAT (Graduate Australian Medical School Admissions Test). So, you not only have to have a competitive GPA for Melbourne, but you also need a competitive score for GAMSAT (if you don't know what this is yet, you should look it up!) - So, it will be a very stressful journey.
This doesn't mean one way is easier than the other, and you should expect any entry scheme for medicine related fields to be super competitive!
I think you should choose whatever is easier and comfortable to you.
I have not done any languages, so i can't comment on that; But! If you were not aware, there are language subjects available and you don't have to do a diploma (Unless you specifically need that diploma for something - but i won't ask).
Also, biomedicine is not the only course you can do to do Medicine.
Bachelor of Science at both, Melbourne and Monash, will allow you to apply for Medicine as long as you satisfy the pre-requisite subjects (e.g. 2nd year level Anatomy, Physiology and Biochemistry at Melbourne).
But, you should also note that, At Monash, 50 spots are reserved for Monash biomedicine students, and only 25 spots for science students - So, there are less opportunities / space for science students
According to my friends who does biomedicine at Melbourne, they seem to find it really intense while i find my course (science) alright - So, Science may be a less intense alternative pathway for Medicine (my opinion of course). This is also something to consider if you find managing stress a little bit hard.