Carbon nanotubes (CNT) possess remarkable physical properties. However, because of their size, they are difficult to handle. Making composites with them gives an alternative way to handle these objects and to make use of their properties at a macroscopic scale. Here, we present a comparative study of the transport properties of PMMA / nanotubes composite films with both SWNTs and MWNTs. At room temperature, the conductivity of the composites follows a pure percolation behavior when increasing the nanotube content. The universal scaling law for random site percolation with a very low percolation threshold (0.3 weight %) is obeyed over two orders of magnitude in CNT content. At low temperature, SWNTs and MWNTs based composites behave differently. While MWNTs composites still obey the percolation law, deviations are observed for SWNTs. The transport properties are discussed in terms of tube-tube contact and charging energy of the tubes.