K&N makes a good product - if you have one now an it's working for you, stick with it. You more than likely wont see any further gains from switching to an AEM. The only thing I don't like about the K&N setup is the oiled filter. Back when I was younger and didn't know any better, I used to add waaaay to much oil to them, and on several vehicles I saw a dramatic loss of gas mileage. Presumably due to fouling of the MAF sensor. Obviously thats not the fault of the system itself, but left a bad taste in my mouth for oiled filter setups.
I like dry filters because of the simplicity - they are pretty much idiot proof. Unless you put them back on soaking wet after cleaning them, there really isn't anything to screw up.