Im speaking for VY's here, so i dont know if it applies to all models, but this was discussed in great detail somewhere in the VY Commodore section and it was unanimous that Kings Springs were pretty crap and that Pedders were the way to go. Kings give a harsh ride, whereas pedders achieve the same height without compromising the ride.
Ive got a set of pedders on my VY SS and Im very happy with em. They were only slightly more expensive than the Kings too!