I'd say that any difference in standard of living between the UK & Australia is much smaller than the differences within either country, & differences in average income fluctuate with exchange rate, e.g. read more
Since there's not a significant difference in incomes, & both are fairly safe, healthy, law-abiding rich countries, I think which is better to live in depends on your personal tastes. If you like big cities, you may like Sydney - or London. read more