Originally Posted by alex0683de

See my answers in red.

Edit: Another thing about AA - the program may actually be better for you if BA transatlantic flights will be a very rare occurrence. You can earn elite status faster through Gold and/or Platinum challenges (search the AA forum for details) and it will be free to join the program. If you have a lot of BA transatlantics though, then you lose out on too many miles (especially status miles). But for only an occasional BA trip, you could go with AA as your primary program and credit BA transatlantic sectors to Alaska to at least earn award miles for them.