I have tried pretty much all of the frameworks out there for pure HTML5, JavaScript, CSS-based development. Sencha creates wonderful websites, but the learning curve is astounding. It is one of the most counter-intuitive development tools I have ever used. I highly recommend that you avoid it. jQuery mobile so far is the best. It is now in alpha, but generally stable and certainly likely to be the standard approach for targeting mobile in the near future based on its architecture, simplicity, and compatibility. I look at Phonegap as simply a container for your app or a good library for simplified access to native mobile features; it augments jQuery Mobile and does not replace it.