For me it's a close match between several of them, depending on your project requirements ..
There is React Slingshot by Cory House, with a good automation and some core features like Redux, Hot Module Load, etc ...
There is also React Boilerplate which would be my choice for an isomorphic react webapp ..
Also this one React Hot Boilerplate by Dan Abramov
And there has been an effort by Facebook to put something out, fast and easy, production ready, with their own easy boilerplate to start up a project with, Create React App
Then again, take a look at documentation, dependencies and scripts on package.json to get a glimpse of what to expect from each other and then decide ..