YUI2 was the first JavaScript library I started with, then I got into a project where I found jQuery code. At first I thought that jQuery's selector-centric method is weird, but I quickly found out that I was wrong. The thing that I love in jQuery is that it feels like HTML and JavaScript. YUI2 is an OO framework and a good one, but to me jQuery feels more like the web.

I seen little YUI3 but as I seen it's kind of shifted into a more functional style than YUI2.