Bilsteins are monotube gas pressure dampers and KW V3 are twin-tube. From what I read, the twin-tube dampers ride more confortably compared to monotubes, while monotubes are better for racing.
Also, Bilsteins (at least PSS10) lower the car quite a bit even on the highest settings, you may want to consider this also. Monotubes have generally less shock travel room compared to twin-tubes, because there is a gas reservoir at the base of the shock. This prevents larger ranges of height adjustability.
One other thing is that KW has a 7-post shock absorber testing dyno on which they test and tune all their coilovers. There are very few such dynos in the world, most of which are at F1 teams.
Also, KW equips Mercedes AMG Black series, so they must be quite good.
I would go with KW. I have not read a single review of someone who did not like them (at least at the beginning). But I did read some stories about spring coils binding, etc. But these were old enough to not be an issue with their current stuff.
Last edited by tscdennab; 11-30-2011 at 06:14 AM.