Personally, I don't think it matters. i got mine from SLP and it cost under $20. I think when it comes to air foils, what ever is cheapest is best. It is not a sure thing that they do anything positve or give horsepower. It is just one of those mods that it is better to do than not do, just incase it does do some some good. So go for the cheapest and not worry about who is the best.
All I know is TPIS claims that there air foil is the best. They claim that it adds about 36 cfm and 11.7 horsepower on average.
Their fast packs add on average 34.5hp. It includes wires, plugs, an air filter, fuel pressure regulator, and an air foil. I dont know which adds the most but that is a substantial increase for those mediocre additions.
11HP my butt! Those airfoils are just like Baumgarner said, besides most of the guys I've talked to are not doing anything to promote good, smooth airflow in the inlet system anyway. Many have all kinds of rigs to get air into the TB and most are causing unfavorable air currents that can actually hurt performance even though the diameter of the inlet is marginally larger. Just providing a large duct to the TB is not enough, you need to also provide a clean, smooth path for the air.