Nottingham stepped motor

I just recently bought a used spacedeck but still need an arm for it. While doing some inquires I can across this bit of information. That nottingham is the only TT manufacture that uses a stepped motor and that stepped motors are the worst possible choice because of 'cogging'. Brushless motors and syncronous motors have some rumbling but do not have cogging and are therefore better. DC motor,with precious metal brushes, eg Maxon are the best. (this last part I think I understand) Could someone explain the sonic effects due to cogging, and is this really a problem with nottingham TTs.