First of all we need to distinguish between WYSIWYG editors (what you see is what you get) and text-only editors using markup languages like Textile or Markdown. While the former try to display all text formatting right in the edit mode and save the generated HTML to the database on submit, the latter require the user to mark up content with shorthand code, which will be saved to the database and not translated to HTML until output.
WYSIWYG editors seem to be a pretty good choice in the first instance. They can be used like word processors and graphics editors: you format text by means of icon buttons and immediately see the results.
In comparison, the text-only editors are more robust concerning user input. Since they filter out some unrequested “cheating” like multiple spaces or line breaks, they help to achieve consistent layouts. Even they seem less convenient at first: most of the developers from the REDAXO team rather use text-only editors when developing websites.
The demo site contains modules using both types of editors: “Redactor” for WYSIWYG and “Markitup” for textile/markdown.
Similar looks, but different concepts.