From my experience, the most important aspect of a single page app framework is the component api.

Here's the doc for ember's: http://emberjs.com/api/classes/Ember.Component.html

Versus react's: https://facebook.github.io/react/docs/multiple-components.ht...

Versus angular's: https://docs.angularjs.org/guide/component

If you compare them, you can see that react and angular focus heavily on component oriented architecture, while with ember, not so much.

Edit: wrong link.