Recently my friend Vinicius indicated me an amazing web site that measure the performance of some of the most popular JavaScript frameworks in your browser and it is excelent both to compare the perfomance of your applications within different browsers or to pick one of the frameworks to use.

The site is http://mootools.net/slickspeed/

Once the page loads, click at "start tests" buttons on the top of the page and it will execute all the tests to compare the frameworks. But remember, the performance measure is relative to your browser, do the test again with other browsers to check their perfomance.

Besides, this very interesting article from Brian Rendel offer a little more information to help you choose among the variety of frameworks.