LAX-HKG fares are generally pretty cheap (routinely ~$400 RT), so your earnings on an AA coded flight are going to be fairly minimal. Example: a $700 AA ticket on LAX-HKG (of which $90 is taxes) will only earn around 3k miles. You really can't do much of anything with that, so unless you plan to continue to fly oneworld on a somewhat regular basis I wouldn't overthink your decision here.

I'd suggest flying the carrier with the best balance of cost, timing and inflight product.

Also, AA food in J and F is pretty dire (can't speak to long haul food offerings in Y on either carrier). CX definitely has a clear competitive advantage on this score. Cabin service on CX is also worlds more consistent than AA. AA can be fine, but it's very hit or miss (more miss than hit, in my experience).