i have been told that it doesnt matter much ...someone told me they got a cheap one from ebay and picked up more hp than a k&n intake. i ordered one from ebay and its supposed to get here 2moro. i will probably do the install this weekend and could tell you if its any good if you want...
JLT CAI, MM&FF did a review of all the popular brands a while back and found that JLT gave the greatest gains on their stock mustang (with tune) during their trials. In addition, JLT doesn't cost as much as the competition for doing the exact same thing but a little better.
2005 Mustang GT, Silver, JLT CAI + SCT Tuner....more to follow