I have just flown 3 long haul sectors on AA and 1 on BA. As far as the seats are concerned, they are similar by way of width, recline etc. Major difference is leather vs cloth upholstery. AA bulkhead seats at window offered 2 windows and ability to get in and out without disturbing seat mate. Maybe BA is same but always fly last row aisle in WTP cabin on BA.
All AA PE seats have decent IFE as they have recently installed PE cabins. BA as you may know depending on aircraft can have IFE of historical interest. I find the selection of movies and TV more extensive on AA than BA. AA has WiFi on nearly all aircraft.
Food... similar, but AA offered a quite substantial second service meal. Not helping my waistline.
While I am BAEC Gold too, I try to book on AA aircraft over BA.
Hope this is helpful. Safe flights and enjoy.