How about some flow #s. I think the stock filter flow best or very close. I bought a PiperX filter over the winter and just for the hell of it blew lightly through it with the air hose, then with the stocker. The stock flowed much more freely than the PiperX. Just my .02
K&Ns are pretty sloppy. If you ever really look at one up close, the rubber mold is a mess and is all wavy around the edge of the filter. Some are ok, but I've seen some really bad ones where the rubber extends a couple of inches onto the filter in spots. You can even see it in the above pics. It probably wouldn't matter to most people, but I'd rather buy the BMC since it's made better.
The K&N I just installed was in no way sloppy or poorly constructed. I went with the K&N over the OEM and the BMC...I heard that the BMC doesn't filter as good as the K&N or the OEM...so I get a bit more power but worse filtration...Well I want good filtration. The K&N doesn't really flow much more over stock, but I can use it for a million miles.