JavaScript Frameworks: Which one???

In today's web development world, there are a plethora of tools/frameworks out there to take advantage of. Since JavaScript has revived itself and become deeply embedded into today's killer web apps, I thought I would take a minute to list and discuss a few popular JS frameworks, and their differences.

• Prototype (http://www.prototypejs.org) - Offers an very extensible library for creating your own JS objects/classes, as well as using a sweet list of functions for Ajax, DOM, JSON, Arrays etc... It is the basis for other frameworks, such as Script.aculo.us and ModalBox.
• MooTools (http://mootools.net) - A lightweight, selective library which accomplishes much of what the Prototype library gives you. Advantage, smaller library size, since you can pick and choose your components.
• Jquery (http://jquery.com) - Similar to the others, but well noted for its DOM and event modification. Jquery is also probably the most widely used library with clients like Dell, Google, Mozilla, etc... It is also sanctioned as Microsoft's platform for ASP.net Ajax and the MVC.

Some frameworks will support use with another, but not all. Tread lightly.

As you can see, all offer similar functionality, but your choice will most likely depend on the type of project you are attacking. I have had to use all three, depending on the client, technology, and existing platforms; so if you already haven't familiarize yourself with what is out there!