Ajax toolkit comparison

Ajax is very useful in Web 2.0 world. What is Ajax?
Ajax is Asynchronous JavaScript and XML.
Now so many different Ajax toolkits online. Which one is better?
Actually, if you doing some search on the web, you will find a lot of different results.
Some one said the Prototype is best, another one said Dojo is perfect.
How can we find the right one for yourself?
Let me compare them.
Now I have five Ajax toolkits here.
1) Prototype
2) Dojo
3) Yahoo
4) Google
5) jQuery
First of all, the learning curve is the most important issue. For the guy who has some php or other language skill, jQuery is the easiest one. You don’t need a lot of time to learn it. After jQuery are, Prototype, Yahoo, Dojo, and Google.
Next is ease of use. They are almost same. Only Google is a little bit weak.
For the file size, jQuery is smallest one.
There are many issue to be compared.

For me, I just choose the jQuery, which can save my learning time.
How about you?