A comparison is made between clad fibers and lens-like guides with parabolic index profiles, from several points of view: delay distortion, beam capacity per unit cross section, ability to negotiate bends, and deterioration of transmission due to imperfections. Parabolic index profile guides and single mode fibers with any profile (approximately rectangular, parabolic, etc.) are equally promising and attractive for long-distance optical trans-mission from several points of view, namely, capacity per unit cross section, delay distortion, and ability to negotiate bends. Nevertheless, their tolerance of imperfections is markedly different. Though insensitive to diameter changes, the multimode parabolic index profile guide is quite sensitive to systematic or random departure of refractive index profile from ideal. On the other hand, single mode guides are sensitive to random changes of both the index profile and the guide width. Both of them produce scattering loss.