Why connect at all? How about just taking a nonstop NYC to Frankfurt flight? I know that AA may not do this, but is it really worth the hassle to connect just to fly one Oneworld (or AA)?

Advantages of taking non-stop:
1) No chance of missing flight due to connection
2) Transatlantic business class the whole way
3) More time to sleep on the plane

Disadvantages of taking non-stop
1) Don't earn miles / status on preferred carrier (which I assume is AA)

For me, this is a no-brainer, I would take the non-stop. I only stay with my preferred carrier if it makes sense, and in this case, it might not.