Redemption may be easier (CX online) but beware that it may also be more expensive (both somewhat more BA miles than AA miles for the same award in many cases, and much higher "fees" since BA adds $$$ fuel surcharges to awards but AA doesn't).

If you're going to earn BA miles much faster than AA miles (say, because you'll use Diners Club and the "annual" 50% bonus offer on transfer of DC points to BA miles), that may make up for it, but if you want to earn a lot of miles by churning the FFP's credit cards, Citi (which supports AA) still allows that while Chase (which supports BA in the US) doesn't.

So it all depends a lot on the specifics of how the OP will earn those oodles of miles you'll need for a CX flight (all the way from the US).