The main reason is because I have lived there. I only visited Sydney for a week and it would be difficult to recommend it based in just a few days. Definitely much nicer weather in Sydney. But it depends in your personal choice.

In my experience I enjoyed the city, its opportunities, wild life , beaches , weather ( yes, I like the odd shower and milder temperatures). Also safe area, great for schools, plenty of green areas to enjoy with kids. Mountain side not far.