OMNET++ can provide more suitable task of designing, building, and testing for users with practical feedback when developing real-world systems.
This will allow system designers to determine the correctness and efficiency of a design before the system is actually deployed
in term of SDN , OMNET++ is designed for prototyping and evaluating SDN-based application accurately at low costly ,it is flexible , scalable , controller and accessible to many users.
That is right, OMNET++ and Mininet are both used for evaluating SDN with accurate results .each one has some features that can outperform the other.in term of the real application , the Mininet is better that the OMNET++ that it provides the realistic setting for SDN-based application , however , OMNET++ is more flexible and scalable . What is the best ,depends on what the purpose that the user needs to use it.