Mobile HTML/JS frameworks in the wild
Frameworks differ vastly in scope: Sencha Touch is huge (over 300 KB), but it also provides the most robust development platform across devices and operating systems.
jQTouch is an interesting beast, but it’s definitely more keyed to creating specific kinds of interfaces for mobile Web apps.
I think jQuery Mobile is somewhat poorly named; it really should be “jQuery UI Mobile”.
One important thing is to remember that smartphones aren’t limited to the iOS and Android platforms; there’s also webOS, Blackberry, Windows Phone 7 and Symbian out there, to name the ones off the top of my mind. This is the whole reason interface-oriented frameworks exist.
Finally, you should always keep in mind that perhaps you don’t need a framework at all.