Popularity should not be the measure you use. If that were the case, jQuery would win hands down.
You should evaluate the needs of your project and see which fits it best. That said, one of the reasons for jQuery's popularity is its versatility. If you have limited time for evaluation that's where I'd start.
I don't have any particular company or specific job right now for which I can apply. I want to be prepared in advance. This is why I want to know which AJAX framework will give me more chances of getting job. I know other technologies like spring, hibernate.