Sencha Touch is the most performant mobile framework that I've experienced. I will admit that it takes some time to get acquainted with Sencha Touch intricacies. If you pay no attention to resource control (primarily: how many elements you are creating without destroying them) you can get a bad experience. Of course, we're talking about apps that don't require a lot of non-traditional components. I think this route is the best choice for fast prototyping of cross-platform mobile apps. And, I think it's the ideal choice, unless you have a large enough team and budget to code out native versions for you target platforms. Here is an example of an app I did for a startup I was working on. It uses CoffeeScript + Sencha + PhoneGap + some custom native plugins for PhoneGap.
When you start to veer away from a top-notch framework like Sencha Touch, you can run into a lot of performance issues that a good framework would take care of for you. For example, your scrollable components should probably be using CSS translate3d() to make use of hardware accelerations; and myriad other tricks.
https://github.com/celwell/wesawit-st2-app
When you start to veer away from a top-notch framework like Sencha Touch, you can run into a lot of performance issues that a good framework would take care of for you. For example, your scrollable components should probably be using CSS translate3d() to make use of hardware accelerations; and myriad other tricks.