From my experience, the ones you mentioned are the most popular ones, but neither is ideal. Sencha is written in Ext JS, which means all your markup, logic and JS are nested in a .js file. There was a great tutorial series done by Drew Neil, I found it extremely helpful but later I decided not to use Sencha because of its complicated nature (especially because of my jquery background). It was also considerably slow because of its verbosity and the formatted HTML always outputted to the screen. On the other hand, comparing the options out there, it's pretty obvious Sencha Touch does an amazing job replicating the native app look. Also, it supports styles compatible with either the iphone or android (as well as its own neat style)
Jquery Mobile is still in alpha, and from my experience it's very bare, which means bugs galore, and the look of it is not as seamless. Try the online demo and you'll notice some of the transitions and effects are definitely lacking. However, you do have the awesomeness of writing in jquery, which will probably make this quicker and easier on you (I do wish they'd started working on it earlier, but it looks very promising).
I haven't messed with JQTouch a whole lot (it belongs to Sencha btw), but it seems very similar to Jquery Mobile. It's also older and I'm not so sure where development stands there.