I live in Sydney and am biased. Whenever I go away for a long time I always miss the ocean and beaches. I love the variety of everything here too. The food is great. Shopping in department stores and along streets. I don't think there is a better all-round city than Sydney.
Melbourne was once voted the most liveable city in the world. It doesn't have as great weather or the harbour etc, but it is well known for great food (esp Italian and Greek), a number of sporting competitions and always being in the shadow of Sydney (haha).
Perth is a small city with great beaches and not much else. Nice enough to live there if you are after a slower pace than Sydney or Melbourne.
Brisbane - Up and coming city that has grown over the last decade.
Darwin - Small city - smaller than Perth, but much more humid.
Adelaide - Slower and cheaper than the big cities.
Canberra - Slow and known to be boring, but good for Govt jobs and being near the snow fields.
Then there are the other main cities in the different states and towns in the country which can be a fantastic lifestyle.
This Government website has information on life in Oz for migrants.