You'll get 9 avios per qualifying pound (this is the amount paid less surcharges and taxes) of the fare, with a few exceptions (holiday bookings). You can use the same credit card you use for AAdvantage and earn some AA miles on top, I guess you get preferential earnings for AA flights on CC spend.

According to How Much Are British Airways Executive Club Avios Worth? (moneygeek.com) - the value of Avios is about half of an AAdvantage mile, so on the face of things you get a little less value crediting as Avios. But it's all about what you use them for as to how much value you can derive from them. If you're sitting on a ton of miles, then you may want to build up an Avios pot as well.