This paper describes dispersion accuracy of various photonic crystal fibers due to changes in dimension of the first ring of air holes require a tolerance of about + or - 2 percent, as it is mostly responsible for the slope characteristics of the dispersion curves. Using FDM numerical method, it is demonstrated that for identical design parameters octagonal photonic crystal fibers can assume better dispersion accuracy and ultra-flattened dispersion in comparison to other configurations such as hexagonal photonic crystal fibers, square photonic crystal fibers, and decagonal photonic crystal fibers in a 1.2 um to 1.7 um wavelength range for communication.