I can see this shaping up to be one of those arguments we have many times on this board similar to the "what oil to use", "what antifreeze to use" and "what wax to use" ones
I think this is another gray area that is up to you. There are Pro's and Con's for both types of products. As long as you stay away from the 'Quaker States' of the world you'll probably be OK.
Incidently my K&N is on its way in the mail