I had written my MERN tutorial using React.createClass and ES5. Later, I created an ES6 version, here's the github repo -- I've put in a good amount of comments within the source itself.
You could compare the two sets of sources and take your pick, but here's my take:
I liked the following in ES6 classes:
But I also did not like the following:
Having said that, I'll probably stick to ES6 since that seems to be the future.