A comparative study between detonation nanodiamonds (DNDs) and carbon nanotubes (CNTs) as low concentration additives to epoxy composites is presented. The dispersibility of the different nanocarbons in resin solutions leading to uniform composite formation is also discussed. Significant increase in glass transition temperature was observed, which were 37 °C and 17 °C for DNDs and CNTs, respectively. Unlike the pure epoxy, the fractured surface of both composites showed resistance to crack propagation. Tensile properties of DNDs and CNTs composites showed enhancement of 6.4% and 2.9%, respectively. The nanocomposites also showed an increase in microhardness by 41% for DNDs and 12% for CNTs, and a decrease in electrical resistivity by 2 orders of magnitude, with the CNTs showing lower resistivity. In general, the DNDs were found to be quite effective and at the reported concentrations between 0.1% and 0.5% and showed superior enhancement compared to the CNTs.