One advantage per post in order to vote for the best advantage.
Ubuntu is for human beings. It is very User Friendly.
The main asset of Ubuntu is that the creators and developers made this distribution easy to install, maintain and use.
It's popular.
Ubuntu has a very large community, giving users much better support than some other GNU/Linux distributions.
It has an easy-to-use package management system.
Ubuntu is truly a developer's operating system (in addition to being a great general desktop OS).
That doesn't mean that Debian and others are not equally fine when it comes to development, its just a matter of preference.
With Ubuntu I have:
apt-get source [package]
access to code, using the familiar Debian build systemThe other thing I like, and why I go with Ubuntu over other apt based distros is the people behind it. Canonical, almost all of the time, does not get invasive with their patches (aka 'special sauce') when packaging upstream code. They also don't do crazy 'cherry picks' from bleeding edge stuff just to get a feature into the next release. Its one of the few instances where things stay current, but not bleeding edge current.
Finally, I like the predictable release cycle, convenience of Launchpad PPAs.
In essence, its all the stuff that makes Debian a fantastic Developer's OS, with the addition of a predictable release cycle, extra polished packages and the convenience of Launchpad.
It just works .
Community
Community is the heart and soul of this distro. Whether you are part of the loco teams or just like to browse the forums occasionally, you will find that Ubuntu's community is vast and friendly.
From the get-go Ubuntu has focused on this aspect, and that is why Ubuntu has gotten where it is today. There is none of that Elitism that used to permeate the Linux communities. This mindset has now spread, however, so Ubuntu isn't the only one with the quality, it was simply one of the first. The code of conduct was Ubuntu's main stance that initiated this.
Usable for non geeks
I'd say it is their intention of making linux usable by non-geeks.
My wife, mother and mother-in-law are all computer-illiterate, yet they use Ubuntu with no problem.
Multiple languages.
Most people I know only speak Spanish, or prefer it, so it is a good motivator that it comes in my native tongue.
The option to upgrade every 6 months or every 2 years, so people that prefer a stable system over a up-to-date one have an option too.
You can buy a computer with Ubuntu preloaded on it
It may not seem like such a big deal but the introduction of cheaper netbooks with Ubuntu preloaded has dramatically changed the Linux community (for the better).
Sure, there have always been a lot of developers using/hacking/extending the Linux ecosystem but there has never been a *nix distro as user-centric dominated community until Ubuntu arrived. With the influx of new users who bought netbooks with Ubuntu preloaded, the community shifted focus from providing the most powerful tools to providing the best user experience on a *nix platform.
What resulted was, the netbooks with Ubuntu being sold appealed to parents looking for a cost effective option when it came down to purchasing netbooks for their kids. Which led to the Ubuntu community gaining a large numbers of younger hackers and introducing them to the open source development culture. If McDonalds taught us anything it was, "get 'em while they're young". Fortunately, for *nix, this resulted in the community getting a massive influx of new blood and the preachy cultist followers of Stallman crawled back into their caves to continue hacking on their niche distros, and the world rejoiced in a sigh of relief ;)~
In short, *nix finally found a way to attract a sustainable user base to feed its developers and bring a distro out of the clouds and onto the desktops of the average user's home.
Side Note: For the generations x and y (about mid-late twenties) having a birthday party at McDonalds when we were kids was about the coolest thing a kid could ask for because you'd get to see some douchebag dressed up as Ronald McDonald in person. Those were the days before Mickey D's had massive kids playgrounds.
<propaganda>It kind of makes you sick to imagine that McDonalds massive sprawling evil empire wasn't built on the backs of hard work but small kids</propaganda>
Ubuntu has very good hardware support "Out of the box".
Many other distros don't. Other distros like Mint and Jolicloud have good hardware support, but they are both based off of Ubuntu.
package management system
I would have to say the package management system is what draws me to Ubuntu over any other OS. Its quite large with alot of different apps, and easy to add third party repository's. Its great.
It looks fantastic
Albeit after years of brown, which would quickly be replaced by horrible themes made by amateurs (remember enlightenment?).
Now, when I'm at uni having people looking at my screen, ever so discretely, I'm quite happy to show off something that just looks so much better than any other (Mac, Windows) desktop.
A somewhat different reason/advantage:
Ubuntu is mainly under control of one person (you know who ;P). He makes the main decisions. And although most decisions are very polarizing, they cause much progress in the Linux world. While other distros crawl like a snail, Ubuntu is like a fresh breeze in the FLOSS world.
Another thing is: Ubuntu makes it much more attractive for commercial/proprietary Software to be available for Linux in terms of making this software more accessible and visible (=> section "For Purchase" in the Software Centre).
And this here is a concluding sentence that says nothing because I have nothing left to say :D