Overview
Ubuntu Linux is a powerful open-source Linux distribution based on Debian Linux and funded by Canonical. It has a great user interface and is highly customizable with all sorts of software packages and GTK themes. Ubuntu has a great developer community dedicated to writing new software and making this pretty great operating system even better.
Pros and Cons
Pros:
Uses system resources sparingly
Ubuntu's idle CPU and RAM usage is lower by far than other operating systems(especially Windows), meaning that Ubuntu can run very nicely on computers with lower specs, and older computers. Because of this, Ubuntu computers can run more user processes than a computer running Windows with equal hardware.
Extremely Powerful Command Line
Ubuntu uses an extremely powerful, easy to learn, intuitive shell named bash for it's command line interface. A good command line is a must for Linux people, and Ubuntu definitely has that. In Ubuntu, unlike other non-linux systems, software can be installed directly through the CLI. Pretty much anything for that matter can be done in the CLI. Ubuntu can also host a super easy SSH server for remote access through the CLI.
GTK Theme Customization
Ubuntu uses a display manager called Gnome, which can have various GTK themes installed for it(including the most beautiful OS themes like MacOS) to change the UI look and feel. GTK themes are available to download from sites like Gnome-look.org.
Good Software Selection
Many developers make software and applications for Ubuntu, although it is not as popular as some other operating systems. Examples of software available for Ubuntu include Visual Studio Code, apache web server, Google Chrome, Blender, Audacity, MailSpring, Firefox, Eclipse, Skype, Discord, VLC media player, Steam, and much more. Ubuntu supports Steam games as well, which is very nice! With a good GPU, any game is playable on Ubuntu!
Home folder Encryption
Ubuntu features a home folder encryption mechanism which can be utilized at installation. This handy feature keeps the user's data extra safe from malicious people.
Cons:
Certain Mainstream applications are not supported
While Ubuntu has a large selection of software, certain applications are not supported on it. For example, Microsoft Office and SSMS have no version for Linux. Although this is a downside, there are other Linux/open-source alternatives.
Popularity
While a small chunk of PC users use Ubuntu as their main OS, the majority of Ubuntu PCs are used as servers for websites and such. Today there are over 60 million servers running Ubuntu. Linux is the main OS run on servers, and out of that a good chunk are Ubuntu machines.