Generally speaking, it seems that the University of Sydney will be relatively better, and will learn more knowledge in teaching and scientific research. The advantage of Hong Kong lies in the time period, and the disadvantage lies in this. If you want to work as soon as you graduate, Hong Kong should be a good choice. If you want to learn more solidly, the University of Sydney is a very good choice. It is one of the eight universities in Australia and ranks high in the world. I hope it helps you.