As an AA Platinum, I would choose Cathay for these reasons:

1.Mileage earning and elite status qualifying points on AA.

2.Business Class check-in privileges and lounge access (especially in HKG)

3.Recognition of your oneworld status by Cathay personnel (in my experience they are the only oneworld carrier where status on another oneworld carrier actually means something) and, if you are traveling on full flights,
increased likelihood of upgrade to Business Class (again, your oneworld status really does mean something to them).