I would suggest you first read back through your own thread: http://www.flyertalk.com/forum/ameri...e-dilemma.html

And this is better off in here: http://www.flyertalk.com/forum/onewo...help-here.html

AA Miles can only upgrade BA flights booked in Y or B economy, or W for premium economy (which are the most expensive fares).
Similarly, BA Avios can only upgrade the highest AA economy fares.
AA has system wide upgrades for AA metal.

You can only upgrade 1 cabin, the best value is booking Premium Economy (World Traveller Plus) and upgrade to Business (Club World) subject to availability. This only requires 50% of the economy miles, so TATL it can be as low as 12,500 avios.

To get lounge access, you need to be OneWorld Sapphire or Emerald (AA Platinum or BA Silver). With AA this is easier to achieve flying economy, however you don't get US Domestic lounge access.

Pros for BA are the upgrades from WTP to CW, Reward Flight Saver European flights, and Lounge access for US domestic
Pros for AA are better earn/burn rates, systemwide upgrades (if you would achieve that status)