Top 5 Javascript Frameworks - Which do you prefer?

Javascript libraries have become fundamental to good web design, almost all ste nowadays have some element of javascript or Ajax present. It is probably the main element in developing the Web 2.0 movement.
There are many Frameworks, which do you prefer?

1. jQuery 

URL: http://jquery.com/.
Blog: http://jquery.com/blog/.
Documentation: http://docs.jquery.com/.

“jQuery is a fast, concise, JavaScript Library that simplifies how you traverse HTML documents, handle events, perform animations, and add Ajax interactions to your web pages. jQuery is designed to change the way that you write JavaScript”.

2. Prototype 

URL: http://www.prototypejs.org/.
Blog: http://www.prototypejs.org/blog.
Documentation: http://www.prototypejs.org/learn.

“Prototype is a JavaScript Framework that aims to ease development of dynamic web applications. Featuring a unique, easy-to-use toolkit for class-driven development and the nicest Ajax library around, Prototype is quickly becoming the codebase of choice for web application developers everywhere.”

3. script.aculo.us 

URL: http://script.aculo.us/.
Blog: n/a.
Documentation: http://wiki.script.aculo.us/.
Note: script.aculo.us is not a Framework by its self but it is an addon for Prototype.

“script.aculo.us provides you with easy-to-use, cross-browser user interface JavaScript libraries to make your web sites and web applications fly.”

4. Moo Tools 

URL: http://www.mootools.net/.
Blog: http://blog.mootools.net/.
Documentation: http://docs.mootools.net/.
Demos:http://demos.mootools.net/.

“MooTools is a compact, modular, Object-Oriented JavaScript framework designed for the intermediate to advanced JavaScript developer. It allows you to write powerful, flexible, and cross-browser code with its elegant, well documented, and coherent API.”

5. MochiKit 

URL: http://www.mochikit.com/.
Blog: http://www.mochikit.com/blog.html.
Documentation: http://www.mochikit.com/doc/html/MochiKit/index.html.
Demos:http://www.mochikit.com/demos.html.

“MochiKit - makes JavaScript suck a bit less”.