Having just finished a large Backbone.js app, I wouldn't pick that either. UNLESS, you're prepared to figure out going in a wide range of other libraries and add-ons you're prepared to mate with it in order to get a solution that really covers a variety of needs.

Backbone.js by itself is just missing so many pieces that the name is a real misnomer. I don't know anybody who could stand up if their real backbone was missing that many vertebrae.