Oh, should mention brisbane: really nice city, good night life, and the gold coast is 1 hour down the highway for good surfing (I've been told about the surfing, but never surfed there). There must be a reason why there's a suburb on the gold coast called "surfer's paradise".
The biggest problem with sydney is the cost of living/housing. Everyone's stressed about money where as in other cities like Brissy, people are a lot more laid back. Even still, compared with the UK, sydney is still pretty relaxed.