Linux Administration for Nerds
Copyright 2018 Brian Davis - CC-BY-NC-SA
Linux is available in a variety of distributions. These distributions start with the Linux kernel and add on a variety of system and user applications.
I started using Linux with Redhat on a Pentium system in the late 90s, SUSE on an AMD K6 and later Ubuntu. Recently I have been seriously using Debian and CentOS while testing Arch.
Generally the distributions espouse different philosophies and different configuration or application packaging formats. Redhat and Canonical, for instance, are commercial companies that sell support services to big companies while releasing free community editions of their operating systems. On the other hand Debian and Arch are organizations of volunteers. The nature of the organization that maintains a particular Linux distribution can have an affect on the software they develop. For instance Debian holds to high standards of democracy and freedom, so they do not provided packages for closed source software (like manufacturer provided graphics drivers) and tend to steer people away from such packages. Redhat on the other hand, as a more "enterprisey" organization generally offers very long term support for it's versions. Canonical, which tries to act more like a startup, has a 6 month release cycle and is often quick to embrace new software. Arch is targeted as a "bleeding edge" distribution, has no scheduled releases at all, users just apply a continuous stream of updates.
Each distribution will come with slightly different schemes for configuring and maintaining your system. Redhat and CentOS will have you using yum to install software, Debian and Ubuntu apt. Redhat was faster to switch from initV to systemd. These differences can be annoying when switching, but any competent system administrator shouldn't find the changes too difficult manage.
Many Linux users like all this choice and will experiment with new distributions regularly. I really liked SUSE back in the day. But the lure of totally free software is strong. I spent a long time wanting to use Ubuntu but after many broken upgrades I just couldn't continue to use it for production systems. I've personally settled on Debian because I feel it has a good balance of a huge library of software that is updated regularly, but not so often that I'm spending a ton of time updating my systems.
CentOS is what my workplace has standardized on. I don't use it for personal systems because it lacks some packages that I want to use, but on the main, I don't find the differences too cumbersome.