I argee, ues OepnBSD!

Seriously though: When it comes to Unix, the choice is limited as of 2017. The last original Unices still actively maintained today are AIX, HP-UX and (Open)Solaris (with its distributions/forks SchilliX and OpenIndiana / Illumos). Others, like Xinuos OpenServer (a renamed continuation of Microsoft Xenix, later SCO OpenServer), were migrated to be based upon FreeBSD, while the BSDs, including macOS, have largely diverted from the original Unix by/around the mid-90s after originally having started as a pure Unix distribution in 1977.

Although the only real "free Unix" is OpenIndiana or one of its siblings, I would recommend to not start with it. While you could probably learn a lot from it, the community is small, so is the hardware support. Recent reviews show that the experience is not that great anyway:

http://www.dedoimedo.com/computers/openi...pster.html
http://www.phoronix.com/scan.php?page=ne...0X-Hipster

So, if you want to just touch the Unix-like world, I'd suggest you to try OpenBSD or NetBSD first, they come close to what Unix once was. If you want a more accessible approach, FreeBSD (or one of the commercial Unices) might be for you - but note that Unix was never meant to be shiny.

Welcome to nixers!