Best all around JavaScript framework/library?

What are your thoughts about javascript frameworks or libraries that you can use all around. For common tasks like AJAX, string alternation or such.
I myself have only used jQuery and fell in love with it. It's simple, lightweight and powerful. Also one reason is because it's in Drupal core and also jQuery UI extends it to really powerful all around tool.
Also I have heard about Moo Tools, YUI, MochiKit and Prototype. I have no experience with those.

See original post by ram4nd