Use your BA miles for MFUs while still crediting your flights to AA; book from ba.com with your BAEC account, then call later and change the frequent flyer number to AA. The best deal is from WT+ to CW, especially when WT+ is on sale. This gives good value for money without forcing you to redeem for award mileage (which takes you further from your MM goal). I would not suggest redeeming BA miles for AA flights if you want to avoid YQ, as you will be charged YQ even on AA operated flights (exception being domestic US flights, but those are a poor value redemption anyway).