A controller is a fundamental component of the Software-Defined Network (SDN) architecture that will contribute to the success or failure of SDN. Although it can be implemented using different open source and proprietary tools, selecting the best would eventually contribute to the success of implementation. Therefore, there is a need to assess and compare other existing controllers for SDN in the market and research domains. In this research, a comparative performance analysis between Open Network Operating System (ONOS) and Open Daylight (ODL) open source SDN controllers is carried out by installing the latest stable version of ODL, ODL-Nitrogen and ONOS, ONOS-Nightingale on a virtual test environment, Mininet. The initial packet latency, average round-trip time and Transmission Control Protocol (TCP) bandwidth, i.e. throughput, are measured with respect to network topology in Mininet emulator using ping and iperf commands. The experimental results show that in terms of latency performance ONOS controller is more efficient compared to ODL controller, ODL controller has better flow-setup latency performance than ONOS controller. Jitter variation indicates that ONOS controller is more consistent and leads to more stable network connection and the iperf measured TCP bandwidth shows that ONOS Controller processing power is better than ODL controller processing power. Overall analysis illustrates that ONOS is more robust than ODL in our setup.