You shouldn't have to install any other plugins for the enhanced UI option. Gravity Forms comes with the necessary JS for this functionality. You don't need to install the "chosen plugin" and in fact installing it may cause a conflict depending on how it was created.
Your issue is likely related to the fact your theme (or plugins) are outputting multiple versions of jQuery on that page. You can't load multiple versions of jQuery on a single page, it can cause problems.
Gravity Forms enqueues the jQuery that WordPress ships with, which is how all themes and plugins should function. Something else on your site is also including jQuery from Google API's.
You need to determine where this code is coming from. I would suggest testing for theme and plugin conflicts by following the instructions here:
Posted 10 years ago on Tuesday November 29, 2011 | Permalink