AA is a no-brainer to me on the LHR-ORD route:
- You get to use the CX and QF lounges at LHR T3 and AA's Flagship lounge at ORD, which offers absolutely outstanding food and a great selection of premium booze.
- BA is currently operating two daily flights on the A380 (with old J Seats) and A350 (with CS). The latter is occasionally swapped with a 777 with old J seating. AA operates a 787 on that route, and AA's J seat is excellent in my opinion.
- Foodwise I lean toward AA, although others may disagree, and AA has a far better selecton of premium booze (e.g. Woodford Reserve and 12-yr-old Glenlivet vs JW Black on BA.)