My personal experience (used Angular JS and EmberJS, before React) -- AngularJS (like Ember) required a lot of Angular _specific_ understanding to use properly, and (_unlike_ Ember) some of those had significant performance impacts. When I switched to React, i felt like there were 3 or 4 API's I needed to understand, and that the escape hatch was easily reachable at all times. There were numerous features I extended deadlines for in Ember and Angular where I would say to my teamates: "I could solve this with Javascript, but how do you handle this in Angular?". Some people are ok with that tradeoff, but both sides feel relatively strongly about that particular choice.
