If you like to make ui widgets to knock your users out then jQuery is where it is. A host of tools come with the basic library but jQuery UI delivers the sort of capability you need to delight your users.
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.