AA. While BAEC is great for J/F flights, it is abysmal for Y, and it sounds like you aren't doing enough flying per year to reach top-tier status on multiple programs. So stick to AA trans-Atlantic and credit all the miles to AA. At the moment the earn/burn rate on AA vs. BAEC gives about 60% advantage to AA. BAEC is bad for earning miles but good for earning status and lets you game the system (e.g. YUP fares credit as F to BAEC and make earning status much easier).