cook2ph: Anywhere, depending completely on your definition of "best". What kind of work are you looking for? What are your qualifications? What kind of atmosphere are you looking for? What kind of activities do you like to do when not working? Do you want to save up a lot of money swiftly, or do you want to have a lot of fun while not spending more than you earn? Etc, etc. (And actually, for most of those critera, you could still end up pretty much anywhere.)
It's also a really hard question for anyone to answer, since most people don't work more than a handful of jobs at one or two places in Australia, so we lack the breadth of experience necessary to say more than "well, this and this worked for me", without being able to quantify and compare with all the other possibilities.
Anyway, for office work, Melbourne is a pretty good city. Lots to do in the city when you stay longterm (even if there's not that many touristy sights), great live music scene, and not quite as expensive as Sydney (though it doesn't differ much). Of course, it isn't as warm as (most of) the east coast...
[ Edit: Edited on Oct 15, 2008, at 2:09 AM by Sander ]