Moving to Australia, Melbourne/Sydney advice

Hello, I have a couple of options to move to Australia, one in Sydney and one in Melbourne.
However first I wish to ask, for someone coming from London, what are the benefits and downside to move down there :)? Any compromise regarding lifestyle? I am sure weather is a great plus there end of the year but I would like to have a more insiders thoughts on this important lifestyle change.
And secondly I would like to know what kind of salary would be confortable, the package I got for both is similar but one is in Sydney and the other Melbourne so would my package be better in Melbourne as cost of living should be lower than Sydney? If yes would there be any downside or benefits to live in Melbourne instead of Sydney? I know this is a very debatable question so any honest advice is appreciated!

Thanks in advance!