Remove the ATAR from the equation and what you'll think you will get. What uni do you want to go to? Don't let the ATAR be the deciding factor. Put your preferences in and then work from there.
That's your answer. There have been so many threads already re: what uni should I go to, consider all aspects such as travel time, what 'feels' better etc.
If you really want to go to Monash and think it'll give you the best opportunities, choose that. If not, choose La Trobe. You have to do the travel time etc. for a good 3 years at least, remember that.
From my perspective (having studied at both La Trobe and Monash), I thought La Trobe was better in terms of community-feel (this was specific for my degree as the CS/IT department was very tight knit). I lived about 10 mins or so from La Trobe and 90 from Monash. I hated the long travel but thought Monash would be best for my future aspirations. This is why research is very important before making a decision like this and understanding the ramifications/consequences as well as potential benefits of choosing one over the other.
Reasons such as prestige or ATAR should not be the sole reasons for your decision making.