It depends on your travel habits in my opinion. If you won't be spending a lot of time flying on QF metal, I wouldn't do it. Further, if the majority of your flying is on cheap Y tickets versus paid J/F, I'd accrue to AA and not QF. QF's program is more geared towards the big spenders and not neccessarily the most frequent flyers.

That being said, QF's elite tiers are more "valuable" than AA's but they're also harder to obtain. If you know you won't qualify for QF Gold, I wouldn't even attempt it.