Just to clear up any confusion, you can only redeem Qantas points through the Qantas portal/website/phone system, but you can use them to book flights on Qantas, Emirates and all of the One World Alliance airines (American, cathay, British Airways, Qatar etc)
Yes USDM is the frequent flyer program of US Airways, in that program there isn't really any ability to 'earn' miles through credit card use or sign up bonuses here in Oz, but you can buy, gift or share miles and it is much better value to do these during their regular 100% promotions, so with buying for yourself or gifting to another member of the program you were able to buy/gift 50,000 miles and the other person would receive 100,000 miles because of the 2 for 1 promo... The same promo would apply to sharing miles you already had to another account, but these were even cheaper to share (about 1 cent US per mile and the other account received 2 so a double up, up to the 50,000mile/100,000mile limit per promotion)...
The way to work out how good the competing programs are is to not only figure out how much it costs to acquire miles/points through things like buying during promotions, earning on credit cards or from flying, but to also then look at their various charts for how much flights cost to redeem in terms of how many miles/points does it cost to get somewhere in the various classes and how much are the fuel surcharges applied when redeeming the award...
Me for instance i earn practically no miles/points from flying, I have no status currently with any airline, i either earn Qantas points through things like credit card sign ups, buying things/paying rent with my points earning credit cards or signing up for other promotions like various insurance products.... For the other overseas frequent flyer programs I am a member of, like Avianca's Lifemiles and US Airways USDM, I buy miles only during promotions... When i redeem these miles/points for award seats i gain no points or status credits (SCs under various names is what allows you to move up through the status levels of programs) but it doesn't matter so much because I usually redeem for long haul business class seats which come with extra baggage, lounge access, priority counters at airports etc, etc...
So there are a number of strategies that you can follow, it can be confusing at first, it may take 3-6-12 months to really become knowledgeable about it all, but just keep reading and askng questions and you'll get there...
