Mootools, Scriptaculous, Prototype, YUI or JQuery?

[eluser]Unknown[/eluser]
Thanks to codeigniter i've seen the how much more efficient it is to use a framework for my php coding. I now want to start using a framework for javascript too. I've messed around with all of the main frameworks, and I think I have a leaning towards jquery or mootools, but have heard good things about all the main frameworks. I'd say my Javascript knowledge was slightly above basic, the most advance thing i've written from scratch was an ajax autocomplete text field, so what are people's experiences with js frameworks and which fits best with codeigniter. I'm mainly doing application development, so i'm more interested in ajax than animation and flashy effects.