I would recommend Dojo over ExtJS for building "web applications", out of the "heavy duty" frameworks Dojo leads the pack by far. If you want to get up and run

I would recommend Dojo over ExtJS for building "web applications", out of the "heavy duty" frameworks Dojo leads the pack by far. If you want to get up and running quick then I would suggest jQuery, it is drop dead simple and extremely light weight. But it can start to fall down (in terms of maintainability) when you are trying to manage a large code base. From a pure employment perspective (what job postings are looking for) jQuery is the hottest followed by Dojo.