The stock SVT Airbox/Snorkel and the SVT Header at the best zetec intake/header combo. A lot of regular zetec guys will swap the svt intake/snorkel and the header onto their cars.
when I had mine i made the mistake of adding an SRI onto my SVT before I did the research. But since i daily'd the car I rather enjoyed the sound of the intake combined with the exhaust I put on it so i didn't' care. Also never did get a tune either which I'm sure would have been a good idea but w/e at this point.
I'm pretty sure unless you went full legit filter in the fender CAI the stock is the best way to go
'04 Audi A4 Avant 1.8T 6MT
'04 VW R32 - (O:o)=R32=W====(o:O)