Based on my experience with AngularJS modals so far I believe that the most elegant approach is a dedicated service to which we can provide a partial (HTML) template to be displayed in a modal.
When we think about it modals are kind of AngularJS routes but just displayed in modal popup.
The AngularUI bootstrap project (http://angular-ui.github.com/bootstrap/) has an excellent $modal service (used to be called $dialog prior to version 0.6.0) that is an implementation of a service to display partial’s content as a modal popup.