If you're based in the USA, I'd go with UA. Far better accruals, status and redemption possibilities than QF, not to mention it's free. It's turning out to be pretty darn hard to get redemption seats on QF on many routings these days as something like 90% of the country flies with them now. I'd also check the redemption and accrual status with QF in relation to AA and ensure that it's 100% on both with no restrictions or weird rulings relating to another partner carrier. (UA's *status* accrues on any Star partner for example - make sure flying AA gets you status on QF as well as the miles etc).
Not quite sure why you think oneworld is the dominant alliance in SE Asia - far from it IMHO. SQ and TG are with Star and MH is closely aligned with Wings. In the far east Star has ANA and soon Asiana as well, where oneworld has CX, which is it's only carrier based in the entire region. UA also have a very large intra-Asia presence as well with their long held fifth freedom traffic rights, mainly through Japan but also I think I've read Hong Kong as well soon. The itinerary you suggested is more than workable on both alliances - and is probably better on Star truth be told. With oneworld, you would need to backtrack from Kuala Lumpur to Hong Kong, then down to Sydney or Melbourne, then across to Perth, as QF offers no service to KUL. With Star, it's a shuttle on SQ to Singapore then one of 3 flights Singapore to Perth with SQ. UA's code with VirginBlue should be by then extended to nearly all of their flights so if you can alter the routing slightly, your backtracking is far less with Star than it will be with oneworld if you enter Oz in SYD and use the UA code on DJ flights to get around Oz and to PER, then continue into SE Asia on SQ and TG (PER SIN KUL BKK) over to HKG, then onto Europe with SK LH or OS.
I also think Star can give you much more in the way of options from your home market as well in future years - UA AC MX "domestically" [or North Americanly if you prefer
], NZ LH SK OS SQ UA BM transatlantic and NZ UA SQ NH TG OZ RG over the Pacific.
As always - read the fine print of the programs you are comparing. Some nasty little surprises in there at times. With the reach of the alliances these days you can basically get anywhere you want on them, albeit with backtracking involved on most of them. I don't like how big Star has become, but for coverage and options, as well as less backtracking because of the range of carriers, they are very hard to beat for frequent world travels. More so with UA's generous (in comparison to Euro, Asian, Oz schemes) Mileage+ FF scheme.