Although I used to like the noon LHR-ORD flight, I now prefer the last one (UA959).

My reasons:

- No panic to get to LHR early in the day
- Easy transportation mid-day
- Uncrowded LHR compared to earlier in the day
- Short lines at LHR
- Every time I've flown UA959 C was not full
- C service was respectable yet relaxed
- Unlike the morning departure, no breakfast for the the full meal
- Immigrations at ORD was uncrowded as the masses had already passed earlier

BTW, if your day was busy, you can take a free shower at the LHR RCC during your wait for departure. Or, better yet, use LHR's London Lounge (also has nicer showers). Or use both lounges if you have lots of time.

Enjoy....