Opting for js.erb
templates offers a simpler approach and encourages the consolidation of application logic within Rails controllers. This is particularly beneficial for traditional applications where javascript plays a minimal role in handling application logic.
In contrast, utilizing JSON pushes you towards transforming your Rails application into an API server tailored for a javascript-centric client application. If your aim is to execute core CRUD actions through ajax calls and minimize page reloads, then this aligns better with the style of your application.
The choice between these two approaches depends on the nature of the application you intend to develop and the specifics of the individual request at hand.