The question is in regard to AngularJS, BackboneJS, EmberJS and the other frameworks.
I have to translate a project from php to javascript and I have to decide, if I
Let me give this another try:
The key behind web-components (and thus Polymer) is, that they are self-contained. You have a web-component somewhere, you import it, and (if you're lucky) it just works, wherever it comes from. The web-component will NOT interfere other components. So doing things like MVC is not Polymers business (although it provides a data-binding mechanism), as this belongs to the process of tying things together. It is considered to be best practice that these kind of things are solved by creating new elements too, that create and react to events. When it comes to the model you code non-visual web-components, that don't have/need a template. TodoMVC has an (outdated) example for that (https://github.com/tastejs/todomvc/tree/gh-pages/examples/polymer).
So Angular gives you a path to follow on how to do MVVM, whereas it is up to you on how to do the "logic" in your app when using Polymer. IMHO Angular is for more complex and rather enclosed apps, whereas Polymer is for any kind of app, that embraces the web. You even can use Polymer, if you're not writing an app at all ;)