Uni is better for dust. Even the racers in the Baja 1000 wrap their k&n filters with a foam uni style sock.
The stock filter should be replaced with aftermarket mod as the stock one lets dust go around them and into the engine.
Here is a free fix that I made, because I have found all of these fixes interesting but have always considered the stock filter to be a very good quality filter and I did not want to switch to a paper filter because the oiled foam filters are superior for blocking dust. This is very simple; check out the attached photo's. I took a piece of scrap 2X4 and cut it to about 5.5" then wedged it in behind the filter and marked it for depth then cut it for depth so that it fit in flush (see 1st photo). Then all you need to do once you get a good tight flush fit that pushes the filter forward nice and tight is trim the 3 posts flush off of the top cover so they just slightly touch or push down on the wood block. Now you have a nice tight seal at the air intake. If you want added air flow around the back side of the filter and air box, just drill some half inch holes in the block, as many as you like, 4 or 5 should be sufficient.
Here is a fix I posted in "Air filter Fix" thread last month if you want to continue using the stock filter and have it sealed completely. It has worked amazingly well for me. I also drilled 5, 1/2' holes down through the block and another through the center going the full length of the block ( not shown in photo ) for good air flow around the back of the filter also...maybe overkill but I liked the end results better. This costs nothing and I think the stock filter is otherwise a very good filter once you get it sealed up tight.