I'm using an M's K&N:
I know there are some articles around looking at which gives the best filtration (I think they say A'Pexi), and others look at which gives the best bhp gain (I think that says HKS), and I know Mighty Car Mods did a test on Marty's Subaru that said the after-market filter actually hurts performance (although I think that a panel filter in the original airbox was best overall, and it was a standard car).
To me those are all a little too simplistic. - The filter needs to be able to remove air-borne particulate matter so that it doesn't get into the engine and damage the internals (I've seen the effect of a "dusted engine" - it's an anchor). The filter needs to be able to flow an appropriate volume of air without restriction; that's where power gains should come from. To some people the induction noise is also important.
I see it this way: The larger the surface area of the filter, the more it can flow overall from the same rate per cm^2. The better the filtration, the less shite I'll get in my engine (so the less damage I do)... and if I've got more surface area it doesn't matter if more filtration gives less overall flow. - Thus I settled on the M's.
It's also worth noting that different filters have different cleaning regimes; K&N say not to clean and re-oil the filter unless it's really mucky. They say that the dust caught in the oil reduces the overall pore size of the filter giving better filtration as more builds-up. I would imagine that the other cotton filters are the same. Foam will deteriorate over time, so you need to periodically check and replace the element; that's why HKS sell spares for them.
I don't know about the metal mesh because I've never looked into them; I'm just not sure that they can provide enough filtration.
