For the overnight eastbound flight, a longer international leg is better to give you more time to sleep (e.g, connect through DFW or IAH). Going from east coast or even northeast to ORD will make the flight too short to sleep much.
For the return day flight, a shorter total flight time would probably be better, but still best to maximize flight time on international leg and have domestic leg be short as possible.
I'm not an expert on which plane is flown from each airport, but the best seat that I've seen is the American 777-300 (77W). I believe this plane is used DFW-LHR.