Kibana is made by Elasticsearch, therefore it is likely the best first pick. I know several large organizations that use this for log data coming from hundreds of thousands of nodes. Would it work with Graphana? Probably, but Kibana seems to come with ES.
Still, if you only want to learn one thing, and you already have Graphana for other stuff you might use that instead. To me, right now, it seems like Graphana is far more popular for a number of purposes, not just to front for Elasticsearch.
I really need get into the applications integration APIs before I can make a more information recommendation going forward.