This paper evaluates and compares a range of optical pulse shapes for long-haul high-capacity dense wavelength division-multiplexed (DWDM) transmission links with return-to-zero (RZ) modulation format, in terms of their transmission performance and characteristics. Performance is compared at both 10 and 40 Gbit/s, using several different types of transmission fibre. Results show that different pulse shapes exhibit different optimal duty cycle and launch power level into the transmission fibre. In addition, the optimum values and the maximum achievable Q values also depend on transmission fibre type used due to the interplay between optical amplifier noise, fibre dispersion, nonlinear effects, and linear crosstalk from demultiplexers. For both 10 and 40 Gbit/s transmission, super Gaussian waveform gives the best transmission performance and largest optimal duty cycle, hyperbolic secant exhibits the worst Q value and smallest optimal duty cycle, and Gaussian is intermediate between for all the transmission fibre types considered.