I assume you mean MX...Maxxis, ITP, and Kenda seem to have the best products out there. If you are talking MX, 18" rear and 19" or 20" fronts will serve you better, and ITP seems to have more size/style selection than the others.
The Artrax seem to have some pretty good reviews, and the rears are similar to Maxxis or ITP. The fronts are better than stock, not quite RZRs or Holeshots though. Can't beat the price, they are a 2 ply tire. They seem alot heavier than stock, and a little heavier than MXR6s. Can't beat the price, that's for sure, I think they are made in Canada, I believe for CanAm/Bombardier.