ITP Quadcross XC's all the way. I've had ITP GNCC, ITP HD, MAXXIS RAZR and Quadcross are the best i've owned. Sidewalls are super tough/stiff, great traction all the way from sand, to hard packed to mud. They are ITP's latest design for sport quads. Check them out.
http://www.rockymountainatvmc.com/productDetail.do?navType=type&webTypeId=138&navTitle=Tires+and+Wheels&webCatId=8&prodFamilyId=26017