There are a bunch of reasons SelectBoxIt is a better choice for single option select boxes than Chosen or Select2:
1. Mobile and Tablet Support - The native "wheel" interface is presented on the popular mobile and tablet devices. SelectBoxIt also allows you the flexibility to write your own mobile detection script in case you only want to target certain devices.
2. Theming support - SelectBoxIt currently supports theming your drop down's using Twitter Bootstrap, jQueryUI, or jQuery Mobile stylesheets. More popular CSS frameworks are in the roadmap.
3. More intuitive search algorithm - Instead of appearing as a combo box, SelectBoxIt does not present a "Not Found" result. If a search result is not found, then SelectBoxIt will look for the next best option.
4. Better event support - SelectBoxIt triggers over 24 native and custom events on the original select box that your code can listen to.
5. Better method API - SelectBoxIt supports over 14 methods, including methods that neither Chosen nor Select2 support (disable single options, refresh, etc)