Which respects user privacy more?
Mint uses Ubuntu repositories. Depending on what you install they're pretty much the same.
But moreover, you cannot expect that the developers of a distro as big as Mint/Ubuntu are aware of the privacy concerns of every package. OK, that is pretty subjective so I'll add an example:
Some people consider Firefox's (and Chromium's) OSCP certificate verification to be an invasion of privacy. That is because you never asked Firefox to check the certificate against the OSCP database, and that database gets to know your browsing habits.
Still Firefox is in the official repositories of pretty much every Linux distro and with OSCP enabled. Hell, it comes by default with most of them.
There are also the APP repositories, which can carter any software. The APP repositories are policed to some extent, just like, for example, Arch's AUR, but there may be a considerable amount of time until a problematic piece of software is removed.
Are both source codes fully and publicly available for scrutiny?
Several pieces of firmware (notably drivers) are closed source.
Flash player, Skype, are other examples of software that is closed source and that can be installed.
Again, it depends whether you actually use these things.
Are rolling release distros safer?
The moral of the story above is that privacy is not something that is maintained by a distro, but depends on what software you run. And, to be on a decent level of privacy (but without going paranoid) you need to be somewhat aware of the software you run.
Of course, pretty much any Linux/*BSD distro is never as bad as the privacy tragedies sold by Microsoft or Banana Corp (cannot say the name explicitly, I'm afraid of performing a trademark infringement :) ).