I've had both KO2s and the ATZ P3s. Of the two, I'm a big fan of the the ATZ P3 over the KO2. My experience may be different than others, but I had one sidewall puncture on the KO2s and noticeable chunks taken out of the tread rubber. This happened with only two wheeling trips on the tires and I'm not the type to abuse things. I switched to the ATZ P3s and have now put more than half-dozen trips offroad on them and have not experienced the same problems.
Truth be told, the KO2s performed extremely well on the road in all conditions (e.g. dry, rain, snow, etc.) and were very quiet. If I spent a lot of time in the snow, I'd definitely pick them over the the P3s, because the KO2s are simply awesome in that area.
On the other hand, the P3s have a more aggressive tread pattern that's a hybrid between an AT and MT tire. They're still quiet, wear well, and perform amazingly well offroad. I liked the Mickey Thompson ATZ on my TJ so much that I replaced the tires on my LJ with MTZ P3s.
As is always the case, what will work best for you depends on how you'll use your Jeep. In my case I was daily driving the Jeep and wheeling it occasionally, primarily on the rocks. To be clear, I still think the KO2 is a good tire, but if you spend anytime on the rocks it would not be my choice.
I'm sure I'm going to stir something up here!