Brackets is essentially dead. They take months to fix the simplest bugs and they have not added new features in years. I loved brackets but its time to move on since its not actively developed anymore. I am trying vscode now but might go back to atom.
As a Front-End developer I never use ES6. Anything you can do in ES6 you can do in ES5, and when you compile ES6 to ES5 it has to ship with some bloat (polyfills) and I see almost no benefits in terms of speed, filesize or coding ease.
Now if you are writing for Node that is a different story, write in 100% ES6.
I was using brackets, but then they pretty much stopped development on it. It took 6 months to fix the simplest of bugs. So I switched to Atom. Personally I like the way Brackets looks better but its too buggy.