Choosing a heavier framework may put you in risk of 'typical', framework-related bugs that often appear. The bugs are not part of the framework, but they are part of the patterns around it.

Discourse 'private topics' leaks (1) are good examples of typical security Rails apps bugs (the result of overusing ActiveRecord). I'm not blaming Discourse, the same kind of bugs appear in other popular Rails codebases (Diaspora, Spree, Redmine).

Ember.js is very Rails-like. I didn't use Ember much, but the patterns look so similar, that it may lead to similar kind of problems as in Rails apps.

I'm not saying that we shouldn't use Rails or Ember. In fact, I'm a big fan of Rails. It's just worth being careful of not falling into the trap of overusing the framework patterns.

The frameworks are best for the infrastructure parts of the app - http, persistence. At the end, it's better that you can control your models. That's the part of Angular that I prefer over Ember - you own your Model part.

(1) http://meta.discourse.org/t/digest-mail-ignores-secure-group... http://meta.discourse.org/t/non-authenticated-users-see-priv...