The seat map on BA.com is the most representative in my experience, although their most recent output for 787-9 is pretty rubbish and A350 and 777 with small first/Club Suite don't even feature.

Seat guru is a complete waste of time for most airlines and rarely represents reality.
BA.com and TheBASource are both pretty good with additional info such as galley and bathroom locations. TheBAsource with additional info about the IFE equipment and seat pitch and dimensions.