Also, there is this post by the author of Sammi.js which the author probably answers this pretty well.
http://www.quirkey.com/blog/2012/09/04/client-side-framework...
Read or try out a few libraries so you can get a feel for them.
For fronted development I use knockout js. Their documentation is very good. The interactive tutorials offer a great way to learn the framework. The framework itself is not vast and you can get started pretty quickly.
Although it is a matter of preference among the devs but I like the declarative binding style of knockout. It felt natural to me.
As far as adoption goes, Angular.js seems to be the big winner.
http://minifiedjs.com/ is also great
For the OP: Most of the frameworks out there have different advantages/disadvantages. Some are relatively easy to just dip part of a project into, while some will completely take over how you structure your project. I would continue learning JS until you really know you could benefit from a framework and why. Don't fall into the trap of looking for the 'best' framework, because there is not one.