Recs.
Updated
The most popular Linux distribution, Ubuntu offers different OS versions for various devices like desktops, servers, tablets and phones. The desktop version, a fork of Debian, 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 the most competitive free OS to Windows and Mac.
SpecsUpdate
Pros
Pro Developed by major company - Canonical...
Linux distros are great but what happens when the developers just choose to abandon their hobby project? Take Antergos for example, one day super polished desktop OS, the next day the lead developer just throws it in! It's better to use a Linux distribution that has financial backing at-least. Ubuntu, Fedora, Opensuse, Elementary OS...
Pro Use it on almost any device
Not just for laptops - Ubuntu was designed with tablets and touchscreen devices in mind, and with phone support on the way. Ubuntu also has Long Term Support releases, as well as a version oriented toward servers, so you can use the same OS at work or on mobile as you do on your desktop.
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 (author) is proprietary
Canonical is focused on making money so you can see many proprietary offers by them and the OS has built-in trackers (Amazon).
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.
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 Custom PPAs required for most software
To get the most software available, user must add several PPAs to the system. That has major problems:
1) Terminal recommended for adding a PPA, which can scare away users
2) A PPA can potentially distribute malware by creating a "newer" version of a package than available in other PPAs, such as the Linux kernel.
3) PPAs must be recreated and re-added with every major system update.
Con Snaps
Extremely bloated non-solution to porting software across different Linux packaging systems. Even the sandboxing is a bad joke, neither secure nor always seamlessly integrated with the system. There is already a solution for the latter, called Firejail. Or even better, there is Qubes.
Con Narrow repos and significant need for third party PPAs
Ubuntu actually narrows down software choice a lot. Especially in the GUI package management application. Searching for additional applications online and adding additional repos for every single additional package is quite tedious. Even worse in case versions don't match and packages don't install or work afterwards.
Recommendations
Comments
Flagged Pros + Cons
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 Lightweight, runs on any low-end hardware it is thrown at.
VERY Lightweight compared to other full featured desktop OS, mainly Windows. On decent hardware, it takes ~8 seconds to boot up, login, and present you a fully functional desktop.
Pro Simplicity
Ubuntu is designed to be used by everyday people. Because of that, Ubuntu has tried hard to make a user interface that's intuitive and looks pleasant and clean.
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.
Pro Has a clean Gnome interface
Gnome has lot of extensions available and can be custmoized rather easily.
Pro Great long term support release schedule (2 years)
This allows for users to always have a new supported release available without long unkown wait times in between.
Con Unstable
Some people pointed out that updating Arch is a high risk affair. And one should carefully read forums before doing it. The same is true about Ubuntu. Making system updates (like it was with 10.04 to 11.04) that screw so many things up became a routine. Even LTS releases should not give confidence that it will work.
Out of Date Pros + Cons
Con Poor Flash Player support
It's one thing to offer flash player packages. It's another, if none of them work with either Chromium, Firefox or Opera, because Ubuntu just doesn't put it where the browsers actually search for it.