Sydney is better, but I don’t think it’s a huge difference.
There’s more startup activity in Sydney, both early stage and those late enough to be paying good salaries. There’s less difference in the number of corporate dev jobs, but it’s still weighted towards Sydney.
Melbourne is trying harder to court the startup ecosystem (by which I mean both startups and the Googles of the world, as well as those that work with both) than Sydney is, and this is reflected in things like government support, but I suspect that’s not enough to outweigh the benefit of the much deeper Sydney ecosystem.