I've got the Bilstein SP's on stock springs. I've had them since April. You can't go wrong with either Bilsteins or Koni's (MS3 specific). The Bilsteins were really designed for the heavier Volvo S40, so they've got stiffer valving than the Mazda3 Koni's. Now the new MS3 specific Koni's have higher rates and my be comparable. The Bilsteins are abit more pricey than the Koni's, but in my opinion, they're a better shock/strut and think the build quality is better. They're both rebuildable. Of course, the Bilsteins are not adjustable, which for me isn't an issue. They're stiff and that's how I like them. No need for me to make them soft for the street and stiff for the track. I don't really track/auto-x the car and I like a firm ride all the time. The Koni's are not easy to adjust anyway (at least the rears aren't). Between my Cobb RSB and the Bilsteins, the MS3 has been transformed. This is the way the car should have been from factory. I'm running stock springs because I feel the car is low enough from factory. I would love it however if someone would make a spring set with 15-20% higher spring rates without lowering ride height, but I don't think that's going to happen. Most people buy aftermarket springs to drop their cars, not for a higher spring rate, so for now, I'll keep my factory springs. I wound up getting my Bils for around $675 shipped, so the difference between the Bils and Koni's was less than $100 for me at the time.