I've always wanted to try out jQuery alternatives but don't really have the opportunity at work.

What does MooTools do better than jQuery? Or is it purely a smaller binary size?

The quality of a library isn't just performance or usability. You also have to consider if other people working on your code base will be able to figure it out and use it.

Even if jQuery is worse than MooTools in almost every way (performance, usefulness, size, etc.) it has a HUGE advantage in that any web developer has used it before, so there's a minimal learning curve when someone new has to start working on your code base.

Furthermore, since jQuery uses sensible practices in terms of API stability and plugins, you can expect performance and coverage to only improve.

Edit: I realize this could have been read as "MooTools is better" but I actually prefer jQuery from every angle. If you're doing something too complicated for jQuery, you need a full-fledged framework, not MooTools.

Yea I'd have to agree with all your points but I meant more of what it actually does better as a piece of software not as a tool that others have to use/understand.