I've read the Sencha Touch docs. I feel its MVC model is very attractive but it seems to has a long start-up time, especially with external JavaScript (eg:map).
Although I'm comfortable using jQuery in a web site, I have concerns about the maturity of jQuery Mobile. (I haven't tested it yet)
I have no idea about Dojo's mobile framework.
Which of these alternatives do you like? Why?
So what exactly are you requirements? Each framework has different several advantages and disadvantages....
Me personally I use Jquery Mobile, which is now at it's first official release. Don't let version numbers fool you, this has been developed 1 year long and actually works pretty good! The others provide different capabilities:
sencha is based on javascript controls - you create the whole layout from within javascript using JSON notation for properties/actions/events
jqm allows you to use your "standard" HTML and enhances it "auto-magically". In my opinion this is the closest to HTML you'll ever get
Dojo is more about MVC and allows a more structured environment. Haven't used it personally so I can't say too much about it...
Hope this helps