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The most popular Linux distribution, Ubuntu offers different OS versions for various devices like desktops and servers. The desktop version is very stable, particularly due to the number of active users, and provides a lot of features out of the box, so you can start working without having to install hundreds of drivers, tools and software first. For a lot of people, Ubuntu is considered the most competitive free OS to Windows and Mac. Based on Debian.
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Pros
Pro Lots of support
As the most popular Linux distribution, there's a wide range of sources for support online if you ever need help, including the Ubuntu Wiki, Ubuntu Forums and the Ask Ubuntu Stack Exchange site. Commercial support through Ubuntu Advantage is also available.
Pro Just works out of the box
Lots of support for hardware, lots of pre-installed software, and a smooth install process means less time downloading drivers, less time digging through configuration files, and less time deciding on software to use just to get up and running. It also means less time digging through forums looking for support.
Pro Dedicated software center
The Ubuntu Software Center offers a GUI interface for installing new apps which is extremely easy and welcoming for beginners to Linux. But it should not be used by more advanced users since the method of installing through the terminal is much faster and easier after one is used to it.
Cons
Con Canonical is not a community effort / non-profit organization
Canonical is a privately held for-profit company, so you can see some proprietary offers by them for products such as Landscape, or their commercial support, Ubuntu Advantage. They also have partnerships with other companies, such as Microsoft (development of Windows Subsystem for Linux) from time to time.
Historically, they also provided an Amazon integration that would use Amazon links when you used the desktop search, back when Unity was the default desktop environment. This has not been included in Ubuntu since the 18.04 LTS.
Con Canonical does not respect Ubuntu users' preferences
In 2012 it became impossible in Ubuntu to move the close-window-button back to the upper-right corner of the window, where it always was before. To the questions of their users Canonical replied that they know better than users where it would be convenient for users to have the close-window-button.
Con Relatively high system requirements
The default GNOME desktop environment is a resource hog which requires hardware accelerated graphics rendering in order to run smoothly, making out of the box Ubuntu unsuitable for low end systems and older hardware. Even mildly aged hardware, you'll get far better performance out of a lighter desktop environment like LXDE or XFCE.