If quality of life is your priority, then stay away from those huge cities if the pay is the same.
If you prefer a colorful night life, commercialized environment, busy life and more career opportunies and most importantly you are able to earn, like, 40% more, you can still make very good quality of life in big cities such as Sydney .
If I were you, I would make the same choice if the salary of the Sydney's position is not at least 40% more.