In this study we examine graphene with different shape, size, functionality and electrical conductivity as carbon nanofiller for epoxy (EP) composites. Thermally reduced graphite oxide (TRGO) and a nitrogen doped derivative (N-TRGO) are compared with multilayer graphene (MLG) derived from milling of graphite. Whereas wet grinding of graphite forms stable non-functionalized MLG dispersions, solvent free dry grinding of graphite under N 2 and CO 2 pressure allows for mechanochemical functionalization of graphite. TRGO and N-TRGO show best exfoliation, highest electrical conductivity and efficient matrix reinforcement at low percolation threshold. As compared to TRGO, wet and dry grinding represent cost-effective routes to MLG and afford EP composites with improved stiffness at higher filler content. These fillers offer great promise for application in carbon/polymer composites going well beyond the scope of epoxy resins.