As BA Gold in AA economy you can choose you seats at the time of booking (or any time thereafter) - both the 'preferred' and the main cabin plus (i.e. no restrictions within the economy cabin). You'll also have complementary 'enhanced' beverages (incl. G&T - but probably of the Aviation-fuel type).

One nice bonus is, where they have them, you'll get access to the Flagship lounges - which IMHO are better than the BA Flounges - less packed, decent food, etc. However, these lounges are limited to their main hubs.