This is a great you tube video: AA / JAL 777 Comparison, comparing the differences between American Airlines and Japan Airlines configuration in their aircraft.
If you’re utilizing OneWorld miles and flying long-haul, you can see the seat differences in each class on the Boeing 777 aircraft. Obviously the JAL seating appears better, especially in the premium cabins, and service will definitely be better on JAL so all things equal, choosing JL over AA is a no-brainer.
I recently just flown JFK – NRT on flight JL 5. You can read my trip review here.