Best tyres always on the back, regardless of FWD, RWD or 4WD.
Understeer can be felt through the steering wheel the moment it develops and can be corrected swiftly by easing off and steering / throttle.
Deceleration oversteer triggered by lifting off or braking on a bend is significantly more dangerous as it takes longer to feel through the chassis and takes time and distance to steer, or even accelerate, into to correct. Bearing in mind that people lift off or brake on bends cos they are either going too fast or have encountered a hazard, the last thing they want to do is speed up again to bring the back end in. More grip at the back reduces the likelihood of unexpected deceleration oversteer.
None of this is to be confused with acceleration oversteer in a powerful RWD car as that can be corrected by lifting off.
People sometimes argue that the best tyres should go on the front of a FWD car, especially in winter to assist with pulling away. Whilst this helps in that particular circumstance, the far greater danger still lies in negotiating bends, especially when decelerating.