Network simulation is the most useful and common methodology used to evaluate different network to-pologies without real world implementation. Network simulators are widely used by the research community to evaluate new theories and hypotheses. There are a number of network simulators, for instance, ns-2, ns-3, OMNET++, SWAN, OPNET, Jist, and GloMoSiM etc. Therefore, the selection of a network simulator for evaluating research work is a crucial task for researchers. The main focus of this paper is to compare the state-of-the-art, open source network simulators based on the following parameters: CPU utilization, memory usage, computational time, and scalability by simulating a MANET routing protocol, to identify an optimal network simulator for the research community.