hey,
i had a pipercross panel filter direct replacement for about a year after buying my GTI last may. It was better than stock but a few months ago i took the leap and got a Neuspeed P-Flo.
i have to say that it is the loudest kit i think is available on the market! You can adjust the noise level simply by how far on or off the tube it is!
me and my brother have the same kit, and his is quieter than mine. It does give you a whistle under hard acceleration and it does make me smile!
it sounds good whether you give it a little throttle or a lot, but sometimes depending on revs may sound a bit like you are blowing on a bottle top. its all good tho.
i haven't had a k&n kit for the golf, but did have one for my previous Fiesta ST. it wasn't as loud as the P-Flo is but its still nice, more reserved i think. similar sounds but i much prefer the P-Flo.