We started in Backbone, then migrated to Angular to mitigate nested view chaos. Latest rewrite drops Angular in favor of React and a bit of Backbone, mostly to reduce the learning curve for new devs. Using React for views is the simplest/most robust stack we've experienced. Easier to share/reuse code, easier to debug.

React with Coffeescript has been super great - dropping JSX lowers the learning curve even more, especially since we already use and love slim, and Coffee/React sort of resembles slim.