ANother point that no when has mentioned is, if your schedule allows it, to take the latest flight out as possible. As has been mentioned, NYC-London is a hair over 6 hours flying time and about 5 hours in cruise. If you take the standard early evening departure out of NYC, you will be landing about midnight-1 AM NYC time. This is the time I usually go to sleep. In contrast, if I take an 11 PM flight, I am ready for bed as soon as I step on the plane. I find sleep much easier in those circumstances. Luckily, the NYC-London market is the busiest international market in the world with dozens of flights. I know that AA, BA and VS all operate late-night deaprtures to LHR from JFK. I'd guess CO and VS have similar flights from EWR.