This image is for Rancher 1.x. For Rancher 2.x, see the rancher/rancher image.
We push updated builds to the registry monthly. Once it goes through additional QA we move the tag to "latest" and create a version without the -rcX in the tag. It is NOT advised to use the Beta tag for anything other then nostalgic reasons. It marks the official Beta kick off version and is no longer updated, all of the new stuff is in latest or if your feeling daring, the RC candidates.
The RC releases are bleeding edge, and may have bugs that prevent upgrading to released versions.