Originally Posted by
Volvic
I'd say AA but be aware that AA and BA have a funny agreement over transatlantic flights. You can earn/redeem only on their own metal.
With AA miles only on AA*, with BA miles only BA.
*it's a bit more complex, e.g. AA miles can be used for London-Canada (i.e. BA)-USA (i.e. last leg with AA). But with BA miles you can not redeem a direct AA TATL, e.g. JFK-Paris.