From Gentoo Wiki
This discussion is done as of October 10, 2018.
It is recommended to stick with the stable branch. However, if stability is not that much important and/or the administrator wants to help out Gentoo by submitting bug reports to https://bugs.gentoo.org, then the testing branch can be used instead.
Not accurate in practice testing packages are more stable then stable since gentoo is rolling release stable packages are outdated, unstable and full of security holes.
Should be updated!
- No. I will correct you here. Unstable packages are described accurately. "Stable" doesn't have anything to do with security patches, or bleeding edge. The information is accurate and good advice for system administrators who actually deal with the needs of production. --Maffblaster (talk) 16:55, 10 October 2018 (UTC)