I'm flying British Airways, Boston to Heathrow (BA238) and back (BA213), in May. The seating maps offered by BA do not correspond to the seating maps offered by SeatGuru, etc. The seating maps BA displays do not correspond with any seating maps SeatGuru displays for any BA long-haul aircraft.
If you've flown this route, what did you find?
Aircraft type also varies. BA shows a 777 on the BOS-LHR leg, and a 747 on 213 back to Boston. The flight trackers I've checked show BA using 787's on both routes. Of course, aircraft used on a route can change during the year.
Seems reasonable to go with the airline, not the third party sites. But...