ive heard the pipercross are sposed to be a more deep noise....k&n are nice, but havnt heard ne good things about green....and green are pretty expensive
i fitted a green cotten air filter, sounds sweet. i've only got a 1.1 and it makes it sound like it actually has power but i know sumone who had a pipercross and along with his exhaust it wud set car alarms off in multistory car parks...was crazy.