Originally Posted by
schalliol
... I'm more likely to get premier there than on BA ...
If you think you might be a candidate for Premier on BA, you probably already know that you can't get it by flying. It's a status that isn't related to frequent flyer earning.
Originally Posted by
schalliol
... I can't envision where to put the BA # in during the booking process on AA.com. ...
If the AA booking process does not ask you for a frequent flyer number while you're booking, there will be a way of inserting a frequent flyer number after booking. One or other of those times will be the point at which to give their BA numbers to AA.