The std airbox design is the best. It oncorporated a much better lead in and radius entry into the throttle body. None of the aftermarket filters offer this and seem to loose a fair amount by not introducing laminar flow into the TB.
Kits which go from a round outlet at the filter to an adaptor for the TB are the worst, like vipers or BMCs
Although, the K&N does use the OE airbox radius part, you are introducing higher inlet temps.