I have a site on Drupal 6. Is it better to wait for the release of D9 or upgrade to D8?
Executing upgrades in Drupal should be gradual. So regardless, you should first upgrade from Drupal 6 to Drupal 7, then from Drupal 7 to Drupal 8 and so on. If you want to skip, the only way to do this is to build a totally new website on a higher version.
As for waiting, you’ll lose a lot if you do not start using the benefits of the “big eight” as soon as possible. The 8th version of Drupal is more powerful and provides your customers with greater user experience due to its mobile-first approach, HTML5 markup, improvements in multilinguality, web accessibility, content editing, and much more.