In my experience, the ones you mentioned are the most popular, but none of them are perfect. Sencha is written in Ext JS, which means that all of your markup, logic, and JS are embedded in a .js file. There was a great series made by Drew Neil , I found it extremely useful, but later I decided not to use Sencha because of its complex nature (especially because of my jquery background). It was also significantly slower due to its verbosity and formatted HTML always being displayed. On the other hand, comparing the options there, it's pretty obvious that Sencha Touch does an amazing job of replicating the look of a regular application. In addition, it supports styles compatible with iphone or Android (as well as its own stylish style).
JQuery Mobile is still in alpha, and in my experience it is very bare, which means errors are abundant, and the look is not so seamless. Try the online demo and you'll notice that some of the transitions and effects are definitely missing. However, you have a great opportunity to write in jquery, which will probably make it faster and easier for you (I would like them to start working on this sooner, but it looks very promising).
I haven't confused much with JQTouch (this applies to Sencha btw), but it looks like it is like JQuery Mobile. He is also older, and I'm not sure where the development is located.