So i'm pretty qualified to make the comparison between the USA, UK and Sydney. I have lived in the US (1 year back in 2001) and Sydney (2 years up till last May).
The best country depends what you're after, it's all personal preference. Personally I go Australia > UK > USA.
Australia is a great place. There is something for everyone like the OP said.
- The people are pleasant. I was expecting some anti-britishness but did not get any beyond the usual good humour between friends and work colleagues.
- The weather is great. Winter is Sydney is often better than the UK in summer.
- I found crime to be very low. I did not see ONE fight despite being out all the time. I still can't believe it!! In 2011 I came home to the UK for 2 weeks and saw about 5 fights just being out and about drinking with friends (Richmond, Bath, Twickenham, etc).
- Their economy is strong and the pay very good.
- More relaxed attitude towards work, generally much more social, outgoing, etc.
- The ceiling for importing goods from abroad is $1000 for items for personal use. This get's around a lot of the 'expensive' issues.
The bad:
- They have a lot of tension between certain groups. There's a lot of hate towards Arabs, especially Lebanese.
- It is expensive there and while the pay is good you realise you're being taken for a ride a lot. A £60k car in the UK is the equivalent of £92k in Australia. The Supermarkets sting you for food and have a monopoly as imports are heavily taxed.