Originally Posted by Speedbird876

Keep checking the seat map. When there is only one window seat left, purchase it. Otherwise hold on until the time you can select for free.

The LHR-JFK probably has lots of cardholders who may be able to choose seats at any time, but frequent travellers probably prefer aisle seats, not windows.

Are you travelling on a day or time when there will be more leisure travellers? These probably won't have advance seat selection.