Having gone through these three frameworks, I’m going to say something I wish other review sites said: For each purpose, there is a “best” framework. It all depends on context.
If you’re building a rich web application from scratch, YUI will have very thorough tools to do anything you want. As long as you survive writing the code.
If you’re looking to add a little ajax and dhtml to your exisiting web page, or need a lightweight, high performance library, go with Mootools.
Somewhere between Mootools and YUI, jQuery has a lot of features and is very tidy to code.
Perhaps we can compare the philosophies behind each framework by examining their respective homepages:
|Comment||Look at how busy and dated their homepage is… but it is compact.||A very slick page, but underneath it, it is a little bloated.||Simple and clean.|