When I'm referring to technical software documentation I mean broadly two things:

• Technical documentation related to code
• Architecture and Design documentation

When considering these types of documentation I favor:

• Plain text
• Versioned
• With diagrams
• Lives near the code

Over:

• Documentation that doesn't exist
• Documentation that can't be trusted due to being out of date
• Diagrams were is necessary a visual tool to modify them
• Lives in another tool/system