Planes seldom drop out of the sky during cruising, even if one of few engines failed, unless and mostly due to someone causing it. Most crucial period is during take off and landing and that's when most crashes happens.
Hence imo, safest place is near the front and back exits, away from wings where the fuel tanks are, although these seats at the wings are the less turbulent. The most dangerous seats are those along, if you draw a line from leading edge to trailing edges of right wing to left wing as these rows are where the other parts of the plane joint to the wing section, which also where the fuel tanks are. These rows are usually exposed when the plane breaks up, hence either you fall off or gets burnt by the fuel.