Best air filters?

The best air filter in the world is one designed for your car, sold by the car dealer that is replaced regularly.

I have read a couple of interesting article on large truck air filters. The gist of the articles was that many truckers are wasting money and actually causing more wear by replacing air filter too often. Most trucks (and my farm tractors) have pressure sensors designed to turn on a warning light when the air filter is contaminated enough to reduce air flow by a set amount. Apparently truckers tend to ignore this and change the filter more often (I know I do on the tractors). The thinking is that a new clean air filter is better than an old dirty one. It probably is from a flow standpoint, but not from a filtration standpoint. "Dirty" filters can filter better than new clean ones.

In the old days restrictive air filters could really screw up a carburetor's balance and make an engine run very rich. For modern fuel injected engines, this is not the case. If you are not at wide open throttle, the throttle plate, not the air filter, will be the most restrictive element in the intake. The engine management system won't care that the filter is more restrictive and your fuel mileage won't be affected. Depending on the design and contamination of the filter, you might experience some power loss, but this will only be at wide open throttle. How often do you drive around at WOT? I know I rarely "floor" my accelerator.

References:

Good advice on number 2 of your list of links.

The best air filter is one designed for your car, and that is replaced at appropriate service intervals.