Now that BA and AA are becoming more integrated in terms of operational interchangeability and BA elites are getting mileage bonuses similar to AA elites (100% mileage bonuses for Oneworld Sapphire-level elites, for example) I don't see much of a downside to sticking with BA. As a non-UK European resident you'd be able to achieve Silver or Gold status (Oneworld Sapphire/Emerald) much more quickly than if you were a UK or North American resident; you might even look at obtaining AA status once you've got BA status.

AA offers one-way redemptions with all its partners, and in general AA redemption levels for premium cabins are more generous than BA's (with some major exceptions.) For the time being, AA is less prone to levy fuel surcharges on some awards than BA; on the other hand BA's MFU (mileage upgrades) are excellent.

Obviously lining up with BA will put you at Heathrow pretty often; AA's transatlantic routes might be more flexible depending on the specific nature of your travel. But I don't think you'll go terribly wrong either way.