The modeling approach is an effective method to obtain the primary line parameters of a transmission line from measured S-parameters. The model parameters are determined according to an objective function with an optimization algorithm. The definition of the objective function is as crucial as the selection of optimization algorithm for the success of the modeling approach as well as the model used. Therefore, in this study, the performances of existing objective functions in the literature were compared for the aspect of convergence rate, runtime, iteration numbers and number of function evaluations by utilizing particle swarm optimization. Due to the necessity of analyzing busbar distribution systems as a transmission line for power line communication, comparisons were made on the problem of obtaining their parameters in 1-50 MHz frequency band. The comparison results revealed that real and imaginary parts of each S-parameter should be considered separately in the objective function to increase the robustness of the optimization process.