This is an old but epic post discussing the pros and cons of each of these frameworks. I’ve been using Backbone heavily over the past two years and this quote really rings true to my experience:
I think Backbone is not a framework, when using Backbone you have to build a framework from the primitives it provides. This can be powerful or a burden and it mostly comes down to how much control you care to have.
In the end Ghost decided to go with Ember and the comments in the GitHub issue makes strong arguments for all three.