As mobile web app gets more and more prevailing, a lot of tools become available for developing mobile web app. In my opinion(I don't know if it's correct), there are two ways to develop mobile web app.
One way is to use some javascript framework such as backbone.js and ember.js combined with some other libraries such as Zepto and iScroll to do this. The other way is to use some integerated toolkit such as PhoneGap and Sencha Touch to write the whole thing. What I want to know is what's the difference between these two ways? How should I choose between these two ways?