When comparing Knockout vs Mustache.js, the Slant community recommends Mustache.js for most people. In the question“What are the best client side templating libraries?” Mustache.js is ranked 3rd while Knockout is ranked 6th. The most important reason people chose Mustache.js is:
Mustache provides you with a clean and easy to understand syntax. Having a syntax that is readable is always a huge plus, since this means easier maintenance and code readability in the future.
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Pros
Pro Easy data binding
Knockout uses HTML5 data attributes to bind HTML elements to data objects in javascript. This allows more work to be done by the framework rather than requiring you to specify where data should be bound in the javascript. The data binding is very intuitive as the bindings are done within the HTML itself in the location it should be bound.
Pro Easy to learn
Has a low entry barrier and an easy learning curve. It's especially easy to learn for beginners.
Pro Built in templating
Bindings in Knockout can also be used to control the generated structure of the HTML. There are bindings provided to allow for iteration and conditionals. The structure of the html reflects the structure of the data so iterative elements are bound to arrays in the data model. Having the HTML structure maintained by bindings keeps the templating simple, easy to read, and maintain.
Knockout also allows for string based templating so you can use whatever templating library you prefer.
Pro Legacy browser support
Supports a large number of browsers, including IE6.
Pro Great documentation
The excellent tutorials with built-in exercises are a great learning experience, even for people without prior MVVM and data binding experience.

Pro Lightweight and plays nicely with other libraries
Pro Dynamic models help with keeping the code simple and clean
Models in Knockout can be watched to keep the page data up to date by using observable objects. The observables notify Knockout when data is changed and automatically updates the page when this happens. By having Knockout maintain this relation, it keeps the front end code cleaner and simpler, and by enforcing a consistent pattern with observables the methodology can be more robust.
Pro Very flexible
One can do a lot of things and it keeps self references and other types of loops under control.
Pro It's only a library
Knockout does one thing, and does it well. It doesn't try to take on more than one area. It does MVVM data binding and that is it.
Pro Simple manageable modules
Using components is a great way of breaking up large modules into simpler ones.
Pro Clean syntax
Mustache provides you with a clean and easy to understand syntax. Having a syntax that is readable is always a huge plus, since this means easier maintenance and code readability in the future.
Pro Available in lots of languages
Available in a wide variety of languages including Ruby, JavaScript, Python, C++, Scala, Go, Julia, Swift and more. See the full list here.

Pro Lightweight
Mustache is easy to deliver. If you need more features down the road, you can switch to handlebars, which is a superset of Mustache.
Pro Logic-less
By design logic-less templates force you to separate concerns thus helping you avoid future problems with refactoring. It also allow templates to be used with multiple programming languages without changes.
Pro Server side support
Mustache.js has multi-language server side support, which essentially means you can use mustache based templates on languages other than javascript. (like if your server-side was built on Java you could still use Mustache.js)
Pro Popular
This would mean that you'll have a large community to help you out if you run into any problems.
Pro Can be compiled
Mustache templates can be compiled to JS files, so that they can be directly loaded.
Cons
Con Slower than others when amount of objects grows
Knockout has a bad performance when the dealing with large amount of objects. You can see more here.
Con Can become complex once the application grows large
Knockout leaves the application structure to the developer and it can become quite complex and unmanageable in the hands of a beginner once the application grows large and complex.
Con Two way binding requires a little extra work
When allowing users to edit existing data, the two-way binding of observables means you'll need to have to save original values before they're edited, to make comparisons or revert if the user cancels the action.
Con Basic tasks are difficult
Mustache js's attempts at making some things simple makes them so easy that they're almost difficult. That is the case with some basic tasks like figuring out how to apply css to shade odd/even rows on your template based content.

Con Bested by Handlebars in many ways
Handlebars being an extension of Mustache bests it in both speed and power. It adds additional features to Mustache which make writing templates easier and faster.
Benchmarks have also shown that Precompiled Handlebars renders in about half the time of Mustache and the rewritten Handlebars (current version) is 5 to 7 times faster than Mustache.
