Flexible transparent conducting films (TCFs) were fabricated using different types of carbon nanotubes (CNTs). Single-walled CNTs (SWCNTs), double-walled CNTs, thin multi-walled CNTs, and multi-walled CNTs have been used to investigate the material effect on the optimal film performance of flexible TCFs. The CNTs were dispersed in deionized water with sodium dodecyl sulfate (SDS) and compared with CNTs dispersed in dichloroethane. These CNT solutions were sprayed onto the poly(ethylene terephthalate) substrate by a spray coater to form CNT films. The quality of CNTs, the degree of dispersion, film morphology, and the performance of TCFs were characterized and analyzed. We found that the SWCNTs are the best candidate to give the lowest sheet resistance and highest transmittance among these types of CNTs. The SWCNT film conductivity was further enhanced by a factor of four with a negligible change in the transmittance in the visible range by nitric acid treatment.