I really don't know about Eibach or H&R other than that I had H&R race springs on my previous car.

I personally consider the KG/MM's fine for everyday driving, I do it all the time. I just asked my girlfriend what she thought (as they tend to be easy to make complain ) Her first words were stiff, then I asked her if they were bearable and she said ya. She never complains about the ride quality when she rides in my car as its not bad, but it's stiffer then she would like for her own car. She drives a Scion TC which is now on Hotchkis Springs

Her spring rates
Stock
F - 150lbs/in = 2.68kg/mm
R - 245lbs/in = 4.38kg/mm
Hotchkis
F - 175lbs/in = 3.13kg/mm
R - 285lbs/in = 5.10kg/mm

S2000 Rates
Stock
F - 3.92kg/mm
R - 5.20kg/mm

I don't know what the KG/MM springs rates are...but seeing the stock rates I would guess they are about 5.5-6kg/mm front and 7kg/mm rear

 

There are 2 springs by Kg/Mm:Race,and SuperSport.
SuperSport are the softest,at 398 lbs.front and 448 lbs.Rear,and drop 0.75" incn all around;progressively wonded but defenitly harder tnan stock.
If you want nice drop and soft springs,get the Neuspeed.