I've heard good things about d2 just a bit harsh on the road and as for tein im sure you are starting to pay for the name a bit as the as the superstreets are no where near as high speced as same priced d2 or bc.
Who runs d2?
I dont mind paying for the name when it means something!
The Teins are harsh as well but IMHO, most (if not all) the Japanese suspension kits are harsh (they have better roads than us).
With suspension more than anything else you get what you pay for.
You didnt say why you wanted to upgrade? is it a track or road car?
You can't really compare Tein and D2, Tein build quality is much better. Can't comment on the ride as I have had those in different cars. D2 brake line support brackets and anti-roll bar brackets in MR2 coilovers were a joke and I had lot's of trouble with them. Anti-roll bar bracket getting loose contributed to losing control and going out of track at 80 mph. Never again taiwanese suspension for me.