On: Announcing Amber.js

[jashkenas]

Apart from evaluating the APIs yourself, and reading the source, the best way to decide is by looking the apps have been built with each framework.

SproutCore (1) has a list of apps halfway down this page: http://www.sproutcore.com/

You can scroll through a long list of Backbone apps here: http://backbonejs.org/#examples

I'm not aware of app lists for the others you mentioned.