I think that in cases where we actually know the permanent "real" URL of a page, we should probably use it. We don't have to worry about it changing, because URLs are basically forever; if we move the page in a future version, we'll have to throw down a 301 anyhow. 

Links.puppetlabs.com is kind of a junkdrawer, and identifying the person who owns a link and getting them to change it has often been frustrating or confusing. OTOH, all of the 301 redirects for the docs.puppetlabs.com site are managed as code, so updating them is relatively easy. (Not perfectly so, since they're in a module stored away from the site content, but you can update them with our standard code contribution process instead of going through the Google Links backchannel.)