I am a fan of the aFe setup. I run their Dual Cone intake on my car and have had great feedback from customers running their filters and intakes on the whole range of BMW's line.
After visiting aFe's factory this past week, I am thoroughly impressed with the amount of R&D and quality that goes into manufacturing each piece. They individually test each intake and filter using a custom built flow machine, dyno and filtration test to ensure back their claimed gains and filtration numbers. All of their filters and intakes are designed, engineered and produced in house using a combination of 3D modeling, CNC machined molds (they own 2 CNC machines) and computerized production line. Have a look at our write up, it will really change the way you look at aFe.
Jlevi SW Tour of aFe's Manufacturing Facility