Is there something like knockouts dependency tracking for backbone? I haven't really got beyond scratching backbones surface (scrolling through the docs), but the abscence of dependency tracking alone would be a big drawback for me.
Knockout focuses more on the front-end - helping you make a sophisticated UI that responds to view model changes using declarative bindings. It isn't as opinionated as backbone about how you should load and save data.
Both approaches are valid; either could be preferable depending on whether you're focusing most on the UI or on the data.