tein. Thus for street use I would think that HKS would be smoother but on the track Tein would be better. Also the HKS are I believe 10 way adjustable the Tein are 16way adjustable. Also the Tein are cheaper than HKS by a few hundred. But the HKS come fully mounted versus the tein which you have to compress and then put on the pillow mounts.
I suggest you buy them both and send me the one you don't like :-)