Personally i dont think you can really go wrong with the selection you have.
Just think about about what kind of lifestyle you want to try out. Obviously if you are living in california at the moment then sydney wont be TOO different, however if you live in most other parts of the states then there would be quite a difference. You could also consider what other areas you want to visit .. e.g: Asia or Europe..
Last year i was trying to choose between Ireland and the U.S .. then once i chose the US i was trying to pick a place within it. Its hard work but a lot of fun! Good luck making a choice
