It matters what type of riding you do. You see, a K&N is a paperlike material, and a UNI is foam. The UNI will block more dust from getting threw it, and also other stuff. A UNI is moreless meant to be for dirtier riding. A K&N lets more airflow threw, therefore, it lets more dirt threw. If you do a lot of muddy, dirty riding, i would recommend the UNI.
A K&N filter is also more matenence, you cannot just throw it into the sink with some some and wash it, you need special oils and cleaners to clean them correctly. With a UNI, it is much like your stock filter, throw it in the sink and wash it.
If you get the foam, UNI filter, i would recommend getting the UNI Foam Airfilter Oil though, it helps a lot.
I ride in extremely dusty/dirty conditions with a K&N clamp on, no lid, & an Outerwears; if oiled correctly a K&N does just fine at stopping debris from entering your motor. They offer the best gain and I have been running one since 2001 with no problems. When I upgraded my piston from stock there was no evidence indicating anything abnormal entering the motor...
When the sun is shining here the dirt turns into a fine powder getting kicked up in the air by the tires making it so dusty that it's hard to see a few feet in front of you very frequently (and if you don't have goggles your eyes get gunked to ****); this is a good test and proof enough for me. The task of cleaning a K&N isn't hard at all - you buy a recharger kit that comes with cleaner and spray on oil, they cost 9$, do multiple cleanings, and are readily available at your local Walmart, Auto Supplies store, or dealer.