What is the best MIME type for JSON content?

I have used both XML and JSON content types when working on webservices.

XML is fairly straightforward. We usually use

• application/xml

JSON though seems to be supporting multiple MIME types.  I have seen these: 

• application/json
• text/json

• application/x-javascript
• text/x-javascript

• application/x-json
• text/x-json

By looking at XML it seems that the correct JSON counterpart is application/json.
But does anyone know what the official standard is?