I'm not dissing K&N in any way, I have one in my car (which i trust as my car is worth much more than my quads)
K&N and Uni's each have there own place in the offroad world.
K&N is more suited for drags, dunes, desert, etc. Its definitely a more free flowing filter, which is both good and bad.
The Uni is more suited for crappier conditions; mud, water, fine dust, etc. it doesn't flow as well, but due to the foam and oil, it definitely traps more stuff.
For my money, its Uni (or any foam filter of your choice). Washing it in the sink, and watching all the dirt and crap come out make me rest alot easier. every time you clean/oil it, its like putting on a brand new filter. Can't say that for K&N.
just my .02