- What are your project requirements?
- Does the framework support A-Grade browsers?
- Is there a core team of developers?
- How mature is the framework?
- How often are updates publicly released?
- How friendly is the documentation?
- Is there an active community?
- Are benchmark tests performed regularly?
- How extensible is the framework?
- Do you like the API style?
Those are all questions worth asking. Their importance varies, of course, but finding the answers to them will help you make a decision. Four questions I'd like to add are:
- How much will the end user need to download if I use this framework?
- Do the other people working on this project feel comfortable with this framework?
- Does the framework force me to change the way I write my HTML?
- Will I need to invalidate my HTML to make full use of the framework?
I'm not particularly attached to one specific framework, however. So far I have ended up using YUI, jQuery, and DOM Assistant, mainly depending on the project requirements and what suits other members of the project team.
Of those three, DOM Assistant is by far the easiest for me to use. It is also the smallest and the one with the least number of features (though a number of very useful additions are in the works). Maybe there is a connection, I don't know.