If you are talking about the Koni adjustables, get those. They allow you to REALLY adjust the valving, as opposed to the pseudo-adjustable Ohlin's.

From what I've heard, Bilsteins are great to. But they won't lower the car as much as the Koni's will. I'm assuming you are using lowering springs to lower the car.

Because the Koni's are adjustable, you can pretty much make them pretty soft or pretty hard. As for the Bilsteins with their monotube design, they are pretty good at absorbing bumps while preventing brake dive/acceleration squat/cornering lean.

If you are going with the Koni non-adjustable, get ready for some MAJOR stiffness in the suspension. They are significantly stiffer in absorbing bumps in comparison to the Bilsteins.