PowerDNN

Upgrade Recommended:  Yes
DotNetNuke 5.x is the newest version of the DotNetNuke framework and has over 40 new features and over 500 bug fixes.  With expanded security capabilities, better content administration, and faster performance, DotNetNuke 5.x is the next generation of the DotNetNuke web application platform.

DotNetNuke 5.x has been thoroughly tested by DotNetNuke Corporation and PowerDNN and is recommended for production.

Upgrade Recommended:  YES
DotNetNuke 4.9.5 is the most stable version of DotNetNuke.  It has better performance and resolves major caching issues that were present in previous versions.   DotNetNuke 4.9.5 is a solid stepping-stone to ensuring that your site remains stable and will be compatible with DotNetNuke 5.x once 5.x becomes a mature release.

All Versions of DotNetNuke that were released before 4.9.5 have known issues and may also contain critical security bugs. If you are running one of these versions, you should upgrade immediately.