Sproutcore is an advanced HTML5 application framework.
From the technical standpoint ember.js is focused on more modularized code and so called semantic-templates for views;sproutcore is more monolithic
Differences between Sproutcore and Ember
I have seen a lot of post where they are claiming that ember.js is much better than sproutcore but looking at the differences i have seen that the widget support is not there in ember.js
When to use SproutCore and When Ember