Depends on the future aspects I am seeking. If it is just about getting up to the pace of DevOps, I would go for the most used platform; though All are useful.
Also, as a FrontEnd dev, I am not really sure if many things would change about how they operate.
As many things are moving toward more and more automation; Docker, Kubernetis etc are there to orchestrate the Server, wouldn't it be making more sense in doing Certification or the courses on these Automation tools?