Among the most promising candidates for mechanical reinforcement of polymeric systems are carbon nanotubes (CNTs), exhibiting exceptional intrinsic properties such as Young’s moduli exceeding 1 TPa and tensile strengths of up to 200 GPa. Nevertheless transfer of such outstanding properties to the polymer composites has been less than satisfactory and has been asserted to difficulties in mixing and the relatively low filler-filler interactions in CNT networks. Recently, bio-based cellulose nanowhiskers (CNWs) have been thought as potential reinforcing nanofillers in polymeric systems, primarily due to their suitable mechanical properties and rich surface functionality. In this study, hybrid films containing CNWs and CNTs were prepared at various CNW/CNT ratios with the purpose of studying the potential replacement of CNTs with CNWs and to probe the hybrid filler network properties. The films, prepared by vacuum filtration of aqueous suspensions, show better mechanical properties for the CNW films than for the CNT ones, most likely due to the strong hydrogen bond interactions in the first case. For the hybrid film systems, with increasing the weight percentage of CNWs, the tensile properties improve above the CNT films. Moreover, hybrid films with 98 wt. % CNWs and 2 wt. % CNTs show tensile properties exceeding those of both pristine films. Electrical and thermal properties of the films are also compared and possible mechanisms for synergistic behavior are presented.