Originally Posted by
Galapolis
H&R upsets the factory balance of the car by making the front springs about the same stiffness as the rear springs. Factory would be rear about twice as stiff as the front (Eibach maintains this balance). H&R also requires more expensive aftermarket shocks like the B8 to work, versus the Pro-Kit being matched to the valving of the Sachs MSport dampers. The Pro-Kit also weighs half as much as the H&R, so less unsprung mass. It really just comes down to the Eibachs being more of a true OEM+ solution, whereas the H&R is firmly in aftermarket territory.
The stiff front springs can make sense in a track scenario, but for the road it's better to keep the factory balance and just install a stiffer front sway bar.