If you are looking to redeem on AA, be aware that AAnytime awards are NOT bookable with BA miles--only MilesAAver inventory is available. That cuts down on the possible inventory of award seats.
Originally Posted by Upgraded!
Were it me I'd probably accumulate on BA through flying and keep an AA credit card so I could accumulate mileage to use for domestic US upgrades.
This is what I do. I live in the US but fly mostly BA long-haul in J, so I accumulate lots of tier points. I have an account with AA and a Citi AA credit card, and use those miles when I need an AA flight that my BA points won't buy me. I also shift my flight-based mileage accumulation to AA as soon as I re-qualify for Gold each year.
I think if I were you I'd keep the AA base.