ignoring all other factors (distance, campus life, melbournes 3+2 model vs monashs 4yr, which uni is better at engineering, etc.) and thinking solely in terms of engineering. Melbourne has eur-ace and washington accord accreditation (amongst others) whereas monash just has washington accord accreditation (amongst others but not eur-ace). furthermore in europe (where eur-ace is most pertinent) the general degree structure there is more similiar to melbournes 3+2 rather than monashes 4 years. in most countries in the bologna zone you need to do 3 + 2 years to become an accredited engineer, hence why melbourne has eur-ace accreditation and most other unis in australia dont. but even then there are people that study the 4 year bachelor of engineering at RMIT and go do 1 year work placements in germany then come back. although idk if they would be able to be considered for the grad roles there without the masters. but in places like belgium, greece, france, and most of europe really, you need the 5 years.
but besides this there are so many factors to consider when picking your uni such as the feel of the campus etc.
good luck anyway