flatbed is best.
From the OM:
On AWD vehicles, it is required that your vehicle be towed with a wheel
lift and dollies or flatbed equipment with all the wheels off the ground to
prevent damage to the automatic transmission, AWD system or vehicle.
If the vehicle is towed by other means or incorrectly, vehicle
damage may occur.
Ford Motor Company produces a towing manual for all authorized tow
truck operators. Have your tow truck operator refer to this manual for
proper hook-up and towing procedures for your vehicle.