How old/what weight drivers? Seems like the flat karts winning are running maxxis pinks/blues. Kids karts appear to be on hoosier treads. I've not gone to too many of the races, just got a kart recently.
At Coody, kids classes are running hoosiers (slicks) in the advanced classes, we run burris in the beginner (treads), others run hoosier (treads). Clone light through heavy are running hoosiers and yellow vegas, I had luck with maxxis (before the bar code) blue I think, but we are running d30's now.