The Linux distro. There are a gazillion versions. There are some of which do deserve a placement here (minimal, mint) but might not get as much press. Each of these distributions are generally kept by a set of maintainers and was created with a purpose in mind.
Over time the “way” one does something may be seriously different from distro to distro. In some distros the “way” one does something may evolve (Ubuntu use of Netplan 18.04. The new method is a substantial change from previous network configuration)
Slackware: Slackware is listed as the oldest maintained distribution. This was probably considered one of the earliest and easiest ways to get into Linux. Later would be the development of the “Distros” where groups of people tended to gravitate to create and maintain a distribution more toward their liking.
Ubuntu is released as an OpenSource release maintained from Canonical. They provide a release every 6 months and maintain a LTS (Long Term Support) version as well.
Cent or Community Enterprise OS. This is a fork of the RedHat Enterprise. Wikipedia as of this writing doesn’t even mention SELinux as a feature – which IMHO is a severe oversight. Cent’s background coupled with SELinux (as of version 7) maintain this a relevant “Goto” platform for enterprise deployment. Especially if you want to avoiding a price tag in the form of RedHat.
RedHat has recently been sold to IBM. It is very well regarded and widely used in Enterprise environments. It’s professional paid support makes it a attractive choice for those looking for enterprise support.
FreeBSD – A long time standard for Servers, Desktop and embeded platforms. More than 30 years old.
Elementary OS A replacement for macOS and Windows. Clean, Stable (based on Ubuntu LTS) has a wealth of applications.
MX Linux – a simple midweight stable OS. Elegant and clean with a simple configuration. This makes for a suitable “desktop” OS.