Your selection of a JavaScript MVC framework can be based on many factors (including specific framework functionality, in-house skills of your development team, and your experiences with previous projects). It is also help to assess the popularity of a project. Although "most-popular" does not necessarily mean "better", it provides insights into wider developer and project adoption which can impact the long term viability of a framework, ramp-up time for future developers, and support and enhancements to the framework in the future.
Google Trends provides a general indication of the search traffic for terms related to a framework. A graph can immediately provide a rather vivid visual representation of relative popularity.
StackOverflow suggests the general supportability of a given framework based upon questions tagged. There are often numerous flags associated with a given framework, but a few examples of the current counts for representative tags (retrieved via JavaScript as you hit the page) provides a hint as to the developer community involved with each.
Finally BuiltWith.com provides an indication of which technologies are actually in use. It has a paid API, but you can do lookups on their web site for free. At the time this was posted: