When comparing Underscore Templates vs Mustache.js, the Slant community recommends Mustache.js for most people. In the question“What are the best JavaScript templating engines?” Mustache.js is ranked 4th while Underscore Templates is ranked 7th. 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 For micro templating
Due to Underscore's optimized performance and ease-of-use it can be deemed as most fit for use in small sections of your code, where you just want a quick and simple template to render your content.
Pro Pre-compilation
Underscore allows you to compile your template once before data is inserted to it.
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 Not a true templating engine
template
in underscore is simply a function which compiles a piece of template into HTML. It's useful for rendering HTML from JSON and it's not very useful when building complex frontend templates.
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.
