If you're driving, anywhere in Australia, because it's the excitement of the trip more than the destination to me.
My first big, big trip was for ten months, a long time ago. Five and a half weeks on a Russian ship (insert obligatory political jokes here
) around Cape Horn, Montevideo and Rio to England. A month or two towing a caravan around the UK, three months hitchhiking and tenting from Norway and Sweden to Greece and all places in between and then a month or so on another Russian ship back through Suez.
That gave me the travel bug and it's been a different trip almost every year since then.
Best trips in Australia? Anywhere, but Tassie and the Vic mountains and SE coast are really nice.
It really depends on what you want from a holiday.
Nearby? New Zealand is a great holiday. A cruise, or Hawaii if you go further.