Well for a start you could provide is with more information to help you such what you want from a university. They are both extremely good universities for Economics. I would suggest putting UNSW first as the atar entrance rank is higher than Sydney 94~ compared to 90~ so they pretty much work down your preferences in order of highest to lowest atar. I personally also think that UNSW has a more modern faculty in relation to Economics, but hey it depends what your looking for in a university.
Why not go to the open days and find out yourself?