I thoroughly tested all the available frameworks this summer and I was leaning heavily towards Ember until I tried actually using it with Ember-data and it was very ugly. I looked online and there was near universal condemnation of it from what I could find. Even Discourse didn't use it! I saw this link and thought "I bet they are announcing a completely new and working ember-data" and was surprised to see it wasn't even a topic in there.
Ember-data drove me directly into the arms of Angular and I haven't looked back. I am completely stunned it wasn't your number one priority a long time ago.