I joined BAEC because of the HHA feature, my partner's daughter was going to be flying a lot while under 18. My main allegiance is still AA, though having got 2/3 of the way to BA Gold I'm putting in a bit more effort (££££) to achieve it, while considering the future of AAdvantage. Not that BAEC is great for earning or redemption (except RFS) if you're not a manic credit card optimiser, so AA would have to go far downhill for me to abandon them.