Fancy select aims to provide complete control over select box styling. Since Select Box's are native OS, the styling options are (understandably) limited
Style Select works by hiding the native select and inserting an unordered list after it. The unordered list has most of the functionality f a native select, but is completely stylable. You can style the new select in the external stylesheet
Not many. Not all of the functionality of a standard select is transferred across and theres very little configuration options. I've built this precisely to my needs, so if i didnt need a feature, I didnt build it.