OS X installer guidelines
"so what would be the 'correct' way to provide it to you, OS X users
  next to main software?"


Either. If the installer is relatively large in size, I've found that it's contained in a dmg versus a pkg, however. Why?


  A .dmg package is seen as a single file rather than a folder of files
  like a .pkg package....The advantage a .dmg package has is that
  larger files may copy much more quickly to your distribution points than
  .pkg packages.


In my opinion (again, from the perspective of the OS X user), dmgs are intuitively easier to use: mount > drag > drop.