I have been using Ubuntu operating system for almost 3 years now. Having good experience altogether. Following are the 7 reasons to use Ubuntu as operating system. Some of them of given 7reasons stands true for other FOSS based distributions like CentOS, Fedora, OpenSuse as well. So not to go in comparison of those FOSS distributions. Just listed common features that ships with it.
1. Get it for free, off course
Yes. No need to purchase license keys. Get free download from the Ubuntu website. Refer Ubuntu desktop image.
2. Easy to update program and packages for their new releases (Synaptic package manager)
Synaptic package manager helps you to maintain installed package updates.
3. Easy to install packages and programs, Ubuntu software centre
This feature ranks very high on my list. One of the best thing Ubuntu provides. One can go to Ubuntu software centre and install programs of it's choice.
4. No need of anti virus software updates every now and then
Virus attacks to be reduced to considerable amount. Most of the virus that spreads around via Instant Messengers and mail links will not have any effect on Linux machines. Apart from this machine does not get slow by time as it does not have any heavy anti virus software installed.
5. Great user experience(Get themes, desktop effects)
Here comes the eye candy user experience. Compiz program can give you almost 30-40 configuration items to be done to the Desktops. 10 out 10 to user experience. Wobbly windows, 3D Windows and Rotate Desktop are tempting.
6. No pirated software issues. Get free updates for newer versions and fixes
Everything you get on your machine is free software so no pirated software installed.
7. Get many useful web application clients and office tools
Get office tools(Openoffice.org), messengers client(All in one - Use pidgin or Empathy), RSS feed reader, Social media clients(Twitter, Facebook) integrated. No need to install separate application for each.