[tock172]

I'm a big fan of Bilstein suspension dampers. I ran them on my E46 330i and on my E36 M3, in addition to several other family vehicles (Toyota & Lexus). I was a huge fan of their construction quality, performance and ride quality. For my BMWs, I have always chosen the sport variants.

My 135i has low mileage and my original suspension is in excellent shape, but I still plan to upgrade to Bilstein Sport dampers with Eibach Pro Kit springs and sway bars. I know it will take the handling to another level.

My only personal experience with Koni was a set of single adjustable yellow dampers that turned out to be defective.

Another cool thing is that Bilstein will rebuild and revalve your dampers. They are local to me in San Diego. I haven't done it myself yet, but I've heard you can even specificy Alpina spec among other things when it comes to valving.