Gruppe M is the best but is also the worst priced :hammerhead: I know Xcede is bringing in the Envy Full carbon fiber system which is 20k.
As for the AFE and Macht Schell they are decent and give you the about the same power as the other at a better price, however you won't get a better engine bay appearance like the others. The AFE system does get expensive if you take the whole kit incl. the aluminium top cover.
However their gains are minimal, i personally think its not worth it. Go for a software upgrade and let that x pipe work even more. The standard intake is a beauty on the M3, it a ram air intake type system and sucks air from two points, just change the filter to a KNN or BMC high flow filter and may be get a set of RPI intake scoops.