I haven't taken any trip to SYD since the pre-pandemic days, but I've got to say having done the LAX-SYD downhill run on both carriers at least a dozen times each in both F&J I'd personally take AA F over QF J rather easily. I thought the service, food, and hard product were all slightly yet noticeably better. QF J was consistently good but I always felt like a bit of a second-class citizen earning on AA elite. What burned me in particular was having my pre-assigned seat involuntarily moved for a QF elite on multiple occasions at the last minute. While there is inevitably a bad crew from time to time, AA FAs on those trips were mostly very senior legacy AA and extremely pleasant.

This said, with the AA F product currently being wound down I'm not sure this is a very informed or up-to-date opinion.