Personally, I haven't run either, but I can tell you the Duratracs are a good all around tire. The company that runs the ice roads up here swears by them for all their pickups, so that should give you an idea how good they are in winter, and they can be studded if you need that (and if it's legal in your area). The only complaints I've heard about them is that they tend to wear quicker than other tires (which is pretty common for winter tires in general, since they use a softer rubber compound that keeps a better grip in low temps), and they have weaker sidewalls than most off road tires (so if I were you, I'd go with a size that has an "E" weight rating and a three ply sidewall, the lower rated ones are only two ply).
That said, the KO2s are a much newer design (the Duratracs have been around since 2009 I think), so they take advantage of a few more recent advances in tire tech. Tread looks similar to the older KOs from a glance, but they've actually redesigned it significantly. Tread life and sidewall strength is supposed to be excellent as well. Only two disadvantages compared to the Duratracs is that they can't be studded (again, assuming that applies to you) and they don't have a huge assortment of sizes on the market yet (but more are coming in March and October).
You might also want to take a look at the Nitto Exo Grapplers as well. They are another new winter rated off road tire that just came on the market last year, and they are very comparable to the Duratracs in design, strength and tread life, etc, and they can be studded if you need it too. Mel even used them for a race last year, and it sounds like they worked really well for him.
Personally, I'm planning to go with 37" tires, so the KO2s will be my only choice (when the 37s are released in March, that is). Before I heard they were coming out though, I was probably going to get 35" Exo Grapplers... and if Nitto were to say that 37s are on the way I might go with them instead.