In my experience AA is about 1/3 to 1/2 the cost of ticketing through QF and BA. It is not that must at the moment because fuel surcharges are low but it will get more again as the oil price hit a 12 month high again today.

The AA RTW desk is excellent to work with and you can ticket through them. AA usually tickets almost anything and according to the rules the need to ticket even if there is no AA flight at all.

Also be aware that if you start with a long flight ex UK you will be up for a hefty APD of easily GBP 100 just for the one departure.