Deciding which is "better" is an opinion where you need to consider the details of the project.
But Angular is a full-stack single-page application framework. This essentially means you can use Angular to create an application where models, views, and controllers reside on the client rather than the server as in a traditional web frameworks like Rails. The client only communicates with the server to fetch data and re-render the view accordingly.
Dust is just a templating engine--but a powerful one. As such, you could use it in concert with Rails or another server-side MVC framework. It does not have the full-stack capabilities of Angular.
The better comparisons would be Angular with Ember/Backbone/other SPA frameworks and Dust with Handlebars/Mustache/other template engines.