Presentation at Advance 2021 - 9th International Workshop on Advances in ICT Infrastructure and Services, held online due to the COVID-19 pandemic in Zaragoza, Spain. Objective of presenting our research (A literature review) on the market acceptance of SDN controllers and their characteristics. Software-Defined Networks (SDNs) have been used in the last decade as a solution to provide greater flexibility in controlling traffic being distributed over a network, promoting the reuse and optimization of network resources. SDN´s architecture decouples routing intelligence (Control Plane) from routing functions (Data Plan/Forwarding Plane), through a component called SDN controller which centralizes the Control Plane. Therefore, it is required that the controller´s performance and functions provide an optimal integration with both Forwarding Devices (Network Elements) and with the support to new applications to be proposed within the context of software-defined network paradigm. Nevertheless, the rapid development of this paradigm and the increasing availability of different controllers within the market makes it difficult to choose a suitable one. This paper compares briefly the top six SDN controllers according to the market preference, looking not only to unveil some theoretical aspects but also to have an insight about their market acceptance.