When I want to edit C# Unity scripts, they open in Visual Studio. It is supposed to provide auto complete for all Unity related code, but it doesn\'t work.
Keep in mind that if you are using the ReSharper tool, it will override the IntelliSense and show it's own. To change that, on VS, go to Extensions -> ReSharper -> Options -> IntelliSense -> General then choose Visual Studio and not ReSharper.