Round the World Ticket or Single Ticket?

Hi Guys.
Me and two friends are planning on travelling to Asia & Australia in March 2013.
Just wanted to get some advice from people who have travelled.

My question is ... Buy a Round the World Ticket from STA Travel or another RTW tour company ===OR=== Buy a one way ticket to Bangkok spend time there and then another one way ticket to Sydney and worry about getting the other ticket when im ready to return???

PS: I understand in need to have certain amount of funds to enter OZ when get a one way ticket. An I have funds for the return ticket.

You can buy multi-city airline tickets as well. They don't have to be RTW. Most of the big travel sites like Expedia and Travelocity sell multiple destination tickets.

I used AirTreks to book my flights and got an amazing deal. I've found they can be hit or miss on the prices though. Sometimes they're super cheap, other times not so much. It depends how flexible you are on dates and destinations...