And see better seatmaps here:
AA 321T: https://www.aerolopa.com/aa-airbus-a321t
B777-200: https://www.aerolopa.com/aa-772-type-2
Those are drawn-to-scale and 100% accurate.

On the 777-200, 17 A/L are the best Economy seats on the plane for the reasons AirborneLocksmith elaborated. Definitely select one of these.

Also, check for Premium Economy.fares.Especially if you need to pay for selecting an MCE/exit row seat which on longhaul flights can get really pricey or select the "Main Plus" fare which includes these seats, the additional cost for Premium Economy is sometimes very marginal. Always select bulkhead seats in Premium Economy (row 13), those have proper footrests and more legroom than the others.