I have a Maxxis IT on my KDX and another one on my KX (was there when I bought the bike). I was previously running a Kenda Carlsbad and prior to that an IRC VE40 on the KDX. Of these three, I liked the Kenda the best. It lasted a good year before getting too rounded off and I got good, reliable, honest traction the whole time. The IRC got good traction but chunked off some knobs almost every ride. The Maxxis feels "slick" and the knobs rounded off pretty quickly. It's not terrible, but it's not great either. Up front, I've been running a Dunlop K490 and just changed it for an IRC VE39. The IRC's doing just fine up front.
Overally, my favorites would be, in order: Kenda, IRC, Maxxis. I'm going to put a Carlsbad on my KX after the Maxxis wears out there.