Ask HN: which mobile framework, if any, to use?

Im developing a mobile web app for iOS and Android phones and Im not quite sure which approach to take.

Here are my options as I see them:

1. Use JQueryMobile or Sencha

I've had some experience with JQM when it was in alpha. I liked the structure and UI "look and feel" stuff, but the built in controls (ListView) were slow and the fixed positioning did not work as expected.

Haven't tried Sencha, but the pure Javascript approach seems abit unnatural.

2. No Framework

This is the most tempting approach, but I don't want to reinvent the weel.

Are there any good mini-frameworks/libraries for messaging/fixed-tabbar/basic mobile ui ?

As an example, I really like the feel of the GMail mobile app, they seem to have the fixed positioning sorted also.

Feedback welcome!