I have a 2000 mustang and I've seen many Cold air intakes that are all about the same in quality. The argument on which is the best filter to use on them is always coming up. I have heard great things about K&N Filters, but I am not positive which is really the best out there.

Honestly it's not really going to matter at all. If your thinking in terms of more HP well, a cold air intake will get you at most 5-7 more horsepower. As far as filters brand doesn't really matter, just buy one that you can clean and then you should be set for a while.

Sorry but please stay away from K&N. Why not try Green Cotton Filters. Green Cotton Air Filters - Home Page

Have used K&N, Ractive and Green and i m very much satisfied with Green .

Read this before you go for K&N:
TDIClub Forums - View Single Post - K & N
ISO 5011 Duramax Air Filter Test Report

You can try once with power extractor engine, it will really help you. If interested then get informations from power extractor.