We have performed a systematic experimental and simulation analysis of the optical frequency combs generated by gain-switching single mode laser diodes, either free-running or subjected to optical injection. The simulations have been produced with a dynamical model consisting of three rate equations that include stochastic noise terms. The model parameters have been extracted from experiments. An exhaustive comparison between the simulated and the experimental temporal profiles and optical spectra generated under a wide range of switching and optical injection conditions has been performed. The excellent quantitative agreement found in the entire range of the explored operating conditions supports the validity of the model for the analysis of the comb generation mechanisms. The detailed maps generated provide guidelines for selecting suitable operating conditions for specific comb characteristics.