Angular scales up fairly smoothly from a small widget on a site to a full SPA. It has two major downsides.
- you're on your own for a lot of app structure
- it expects you to know javascript quirks about object references, prototypical inheritance and how to read JS stack traces
So Ruby on Rails developers find it quite unfriendly -- few conventions, very different rules about passing data around.
Ember.js has more structure, but it's difficult for a new user to use without something like EmberCLI (http://www.ember-cli.com/) to generate the basic app. It's incredibly frustrating without it since nothing will work until everything is named correctly.
Personally I find it's much easier to get things done in Angular.
However because you can learn Angular by muddling through the docs the community isn't very deep. Ember developers need to keep in touch with each other to understand the ideas behind the framework and changes to it.
So Ember meetups are much more interesting.