These are trade-offs you have to decide between based on your experience and the details of the project. Also, note that Backbone and Marionette are much newer technologies, so you may find less documentation and helpful websites, but you may also find more people excited to work on that project since they get exposed to those technologies. Since you already have a REST API, I'd probably lean toward the Backbone type approach. Obviously, all of this is just my opinion based on my experiences working with these technologies. There are certainly other approaches and technologies that you could consider also.