I haven't used either yet myself, but I can tell you that the miners and people that maintain the ice roads up here have sworn by the Duratracs for years. That's mainly because up until this year they have really been the only winter rated off road tire, and they have had proven excellent performance in ice and snow. They even let you add studs if necessary. That said, the biggest complaint about the Duratracs I've heard is that they have weak sidewalls that can't take quite as much abuse on the trail. I've heard of people running these year round down south, but if you don't need them for their winter performance, I think there are better tires out there.
The KO2s are a much more modern design, not just considering that they are brand new. I've yet to hear a side by side review with the Duratracs, but I do know that their sidewalls are designed to be much more durable. I think their only big draw back (for those who live in an extreme winter climate anyway) is you can't stud them.
Also, have you looked at the new Nitto Exo Grapplers? They also came out this year, and they are very comparable to the KO2s in terms of design. They can even be studded like the Duratracs. I was actually leaning towards getting these until I heard that the KO2s will be sold in a 37" size in the spring.