The vast majority of visitors arrive and depart Sydney. This is not always the best idea, particularly if your trip won’t bring you back to Sydney. Finishing a trip in Perth only to fly back to Sydney to fly to Singapore means a 4 hour flight to Sydney to take a 8hr flight to Singapore rather than just taking a 4hr flight to Singapore direct from Perth.
Some distances to get you started:
Sydney to Perth 4110km or 2550miles (4 hours flying time), Sydney to Cairns is 3143km or 1950 miles (3 hours flying time)
Sydney to Melbourne is 9 hours if you drive up the Hume Highway, and see, well highway, or you could take a couple of weeks and actually see the gorgeous coastal scenery along the NSW and Victorian coasts on the Princess Highway.
Which is to say planning a trip across Australia and ending up in Perth doesn’t necessarily mean that you should return to Sydney for your international flight. Now that mainstream airlines have started to price tickets as two one-way tickets its no cheaper in general to buy a return ticket.
In general your route options for arriving and departing Australia are :
flights from Europe via Asia: major airlines which fly to Sydney, Melbourne, Brisbane, Perth include Qantas, Air New Zealand, Singapore Air, Malaysian, Thai, Cathay Pacific, Japan Airlines . These airlines fly Australia via their Asian hubs (e.g. Hong Kong, Singapore or Bangkok), normally a free stop over and some will continue on to New Zealand with a free Australian stop over. The budget airlines of Asia are now expanding too so that its worth checking out Air Asia X, Oasis Air, Tiger Airways Virgin Blue(which also does internal Australia, New Zealand flights)
flights from North America via the Pacific: this route is still not open for competition so your options are more limited and include Qantas, Air New Zealand, United and Virgin Blue. Flights are typically to Sydney, Melbourne, Brisbane and possibly Cairns There are other indirect options via Pacific destinations such as Fiji, Hawaii, Tahiti but are more expensive and only worth it if you wish to stop off.
flights from North America or Europe via the Middle East: Emirates use Dubai as a hub and fly direct to the east coast USA – Dubai and direct to Perth as well as Melbourne, Sydney and Brisbane
flights from New Zealand: Qantas, Air New Zealand and Virgin Pacific have the most flights direct from Auckland, Wellington, Christchurch to Sydney, Melbourne, Brisbane Cairns, Adelaide and Perth (direct only AirNZ)
flights from South America:are limited and expensive – your option is basically Aerolineas Argentinos from Buenos Aires, via Auckland to Sydney and LAN Chile/Air New Zealand from Santiago via Easter Island and Tahiti.
Budget Long Haul Flights. Its now possible to fly around the world on budget airlines its a fast developing area which is all good for the average cost of airlines as often your full-service airlines will match the budget price anyway! However check out this link you want to persue this option