Originally Posted by PsiFighter37

Hard to say. I would imagine that EWR-LHR is a flight that would be prioritized to depart relatively close to on-time (say, vs. a UAX flight that will get delayed when bad weather happens). If you want a nicer (i.e. less crowded) airport experience, later is probably better. But I have historically tried to take the earlier flights in the evening to LHR because, at least in the past (i.e. pre-pandemic times), clearing immigration in Terminal 2 at LHR could be brutal if you did not get gifted the FastPass by being in Polaris.