Decaflon

For me, I like Prototype.js and YUI. I've fooled with several others, but have stuck with those two.

I've been using jQuery and really enjoying it. It's so much more concise than plain Javascript! I love being able to select elements using CSS syntax.

I dont think I could pick just one - I tend to use whichever suits the current project best.
Each has their own benefits...for example

prototype :
ease of use, power and integration with many other libraries (like script.aculo.us)

YUI :
I use their reset.css on pretty much every project now. Javascript wise I love their event library and am in the process of (slowly) creating an effects library based around its animation capabilities.
If/when i get it complete YUI will prolly replace prototype as my most used.

Mochikit :
I adore their logging/debuging framework (inspired my own javascript logging/debugging script) and the amount of documentation is amazing. But havnt really explored more than that.

JQuery :
I used it for a while and was impressed by just how easy it was to reference different DOM elements and create simple effects.
Havnt really given it the time it deserves tho but will probably return to it later.

I use the dojo toolkit. It is very powerful and beautiful to work with. I haven't had either the need or opportunity to try the others.

Explain to me what "the hell that is the YUI library?" What exactly did you walk through before you gave up on the most heavily documented js library and decided to bad mouth it?

Dustin: I mean the syntax is clumsy and ugly. I also had a horrid battle with some of the drag & drop libraries. I read documentation for 2 hours, and troubleshot for another hour and finally gave up. When I learned prototype, I was delving into code right away.

I understand YUI may be very well documented, but in terms of code aesthetics, performance, and real-world usage, I've found it to be the worst of all the frameworks I've used by far. Until I see more developers (that aren't Y!ers) using it, I don't see a reason to revisit my bad experiences.

I honestly dove into prototype/script.aculo.us just because at the time it seemed to be the most popular (so why not). But now I've been using it for a while, and love it. So many nice little shortcuts, and I've been quite pleased with the AJAX helpers.

With script.aculo.us, I've only really used the effects.js file (which I use all the time), but I'd like to start playing with their other stuff soon.

I'm new to frameworks and I find it difficult to choose which to learn. After reading up on JQuery, it sounds like the best thing since sliced bread.

Does this mean that Prototype is going to be even yummier? I look forward to it.

I've never used Prototype or YUI-JS extensively, but I've recently started teaching myself JQuery by simply making things. It's amazing how simple this framework is to use, so try it out.

Also, I find Prototype to be way to bloated, at least in comparison to JQuery. :)

Holy mother of Christ..! Would you like fries with that bump?

It didn't exist when this thread started (well maybe it did), but Mootools is pretty awesome.

@Oli: Really? Wow, I just did a search on Javascript, as I was looking for some tutorials or such on JQuery. :)

The first library I used was Prototype, but from there I moved Mootools because I love how lightweight and clean the code is. Mootools is what I currently use the most, but I have started testing out jQuery and Ext. Ext is pretty slick but its kind of difficult to find what I'm looking for sometimes in the docs. jQuery I've never been a fan of mainly because the source code is pretty ugly, but the design of it is well done and is what interests me. YUI is actually a pretty good library, but something I'd only use for large-scale projects. The benefit of YUI is the level of quality of its documentation.

Yep, actually... I've morphed from the time I started this. I almost exclusively use MooTools now. EXT looks tempting, but from a licensing point of view -- I just can't wrap my head around it. $5k for a js framework? No thanks, MooTools is good enough for me!

jQuery is actually my preferred framework, with a close second to scriptaculous (I purposely left out the periods).

scriptaculous was the first I actually started coding with, and I grew into jQuery by way of Drupal 5 including it in the core of its CMS. Since then, I've had no real need to use anything else.

I am a bit intrigued by the new jQuery UI that was recently released. If it can ultimately perform like YUI without the bloat (IMO), I think I'll get into using that extension of the library as well.

I use jQuery, but I'm bound to say I've never tried any other framework.
But all frameworks are much more easier than plain Javascript. :)

I've been using mootools lately and enjoying it quite a bit.

itching to use mootools - have been reading lots of good stuff about it.

I've used mootools, prototype, yahoo ui, and jquery, and I definitely prefer jquery.