Switching to BA will give GGL and all its benefits, tonnes more Avios than AA miles on the same flights so appears to be an obvious choice. However, as noted, redemptions on BA will almost always involve a large (for me!) cash outlay. I suspect the amount of cash involved might not be such a burden, but you've already shown a dislike to the BA-applied surcharges on AA redemptions.

Ultimately, we play the frequent flyer game for two reasons: better treatment/ benefits when we fly, and on this count, BA appears to be the general winner, and secondly for redeeming points/ miles. I still think AA is the winner here. Your flying will earn enough AA miles to redeem decent amount of comfortable flights every year.

If you do decide to stick to AA, diversifying with Star Alliance may not be a bad idea: always good to have more than one form of currency, but getting to where you want to go on anything except UA may not be so straightforward.

tb