In the 21st century there has been many distribution (in short, Distros) of Linux Os. Up to now there can be several hundreds of linux distros.
What are Linux distributions?
Linux distros are a collection softwares (mainly Open Source) on top of a Linux kernel. It can bundle server softwares, system management tools, documentation and many desktop applications in a central secure software repository.
Examples of Popular Linux Distros:
Ubuntu’s aim was to be an OS which uses graphical Linux desktop without the need to use the command line; allowing people with not much experience with the command line to use a Linux distro. It started when canonical sent out free CDs with Ubuntu Linux in 2004 and quickly become popular among home users.
I would highly recommend using Ubuntu if you want to move to open source and start using Linux.
It is a billion dollar company which brings an enormous contribution in developing Linux. They have hundreds of specialist to provide support and their products (Red Hat Enterprise Linux and Fedora) are distributed for free. Unlike Fedora which is updated faster but without supprort, Red Hat Enterprise Linux (RHEL) is well tested before release and support is available to 7 years
Debian does not belong to a single company, instead, there i team of well organised developers that elect a Debian Project Leader every 2 years. This distro is seen to be the most stable one and the basis of every release of Ubuntu. It comes in 3 stages: stable, testing and unstable.
Which distro to use?
Since there is a variety of distros there might be doubts about which to use or which to start.
In my personal opinion Ubuntu would be the best to start with since a negligible knowledge of command line is required and it uses a graphical user interface.
It all depends on what does one want to do; for example, Kali Linux is highly used for Hacking and Linux Mint is used as a personal graphic desktop to play music, movies and games.
If one only wants to practice the command line then I would recommend using CentOS minimal.
Below are some links to help you choose which Linux to use: