For a spring setup on the m3 I recommend eibach.
It's basically identical to stock with a feel of slightly less body roll and I noticed a bit heavier and tighter steering feel (before and after alignment eas done)
I was a skeptic of springs only, but now am a believer at least as far as the m3 is concerned.
2009 AW E92 M3 DCT
RAC RG63 w/ AD08R / OEM Competition Package Suspension Retrofit / Akra Slip On