If you're from down under and therefore in QF's program, the AA-BA trans-Atlantic bit won't affect you. You get points from either.

I'd go for BA on most counts, especially if you're in a 777. OTOH, if you can get 26A or 26J on an AA Airbus in coach, there's an entire row missing in front of you for the exit door. 26B and 26H (there is no 26I) are almost as good, especially if you like aisle seats: the space is occupied by a folding rear-facing flight attendant jump seat that's usually flipped up in flight. Leg room in any of those, except for B and H when a jump seat is occupied, beats anyone's business class. You still have a row in front of you - WAY in front of you - to stow stuff under, not a bulkhead.