I find that the flights to LHR are pretty short - so when I take the evening departure, I don't really rest on the plane, and when I arrive in London, I feel tired and eventually become jet lagged. The daytime flight is more to my liking - if the sky is clear you'll get a good view of the Deelmarva peninsula as the flight reaches cruising altitude, they serve a hot breakfast in Y and you can do some reading, and watch movies on PTV. It's really the best way to go...