Selenium being an open-source testing framework, doesn't have any official certification body. And just like every other open-source tool, Selenium also has a dedicated community that works behind keeping Selenium updated and fixing millions of problems of Selenium end-users.
The best certification for Selenium is the one that offers you industry-leading training and project works that help you put the knowledge gained in real-time. The instructors of these training must be experienced and competent enough to guide you through the framework. And the last point, but one of the major points, is that the package must be comprehensive. Selenium Certification course from Intellipaat is the best and the one I will recommend. You can also watch a learner's (Malliha Saad) testimonial on the quality of the course we offer.