Thank you, interesting observations. Other than going to and from Canada, I've used AC for one-stop connections from LHR to US non-gateways when UA and *A were still my major home in the sky. I would add the following pluses for each airline:

AC
Better international Economy product (food, wine, IFE).
Flights to HAV (not AA's fault that they don't, admittedly)

AA
100% mileage earning on all fares.