Very broad question )
Very 9 and 10, and now 11 (coming shortly) has many many new features and fixes for the issues of the old version. You have all the reasons to always update to the latest version.
Version 9: ERPNext Version 9 will be released on 26th September 2017
Version 10: ERPNext Version 10 has been released ! 🎉 🌲 ❄