@JC45 it really depends on your situation and what you want.
Sydney's cost of living (e.g. accommodation, public transpo, etc.) is much higher than Melb (ridiculously expensive). Weather wise, Melbourne is much colder compared to Sydney.
I live in Melbourne, I liked it here and to be honest I was offered jobs with good pay in Sydney in the past but I did not accept.
Melburnians are nice, food/fashion and sports capital of Australia, heaps of places to go, things to do. It is a big city but you don't feel like it's so busy. Lots of laneways with cheap and good food. Vibe here is different I should say.
If you have the chance, I guess the best way is for you to suss out the two cities and decide which one suits you