I'm afraid I can't give you anything informed ... as I haven't used either of them in anger.

That said, they take a very different approach: less about data modeling and events, and more about binding JSON structures tightly to specific DOM elements. I have my own concerns about if it's possible to build truly high-performance web applications with such a granular scheme -- for example, Knockout.js calls JavaScript's "eval()" on every "data-bind" attribute in your HTML. But without someone taking the time to port the same app to all three libraries, and then evaluating it with benchmarks, it's all just speculation.