1. Windows
1.1. Pros.
1.1.1. There is a huge selection of software available for Windows.
1.1.1.1. New node
1.1.2. If you crave the latest in PC gaming technology, then you need Windows.
1.2. Cons.
1.2.1. Compared to other operating systems, Microsoft security is weak.
1.2.2. For people who are used to dealing with Windows, rebooting and re-installing are such a regular occurance that most don't even give it a second thought.
2. Ubuntu
2.1. Pros.
2.1.1. Free, open source, stable, fast, less bugs, more secure, hardly crash , virtually no viruses or malware.
2.1.2. Big supportive communities.
2.2. Cons.
2.2.1. New and latest hardware normally do not support Ubuntu right away.
2.2.2. Many Windows video games cannot be install with Ubuntu.
3. Mac OS X
3.1. Pros.
3.1.1. Airdrop makes sharing much easier.
3.1.2. Versioning keeps track of modification history.
3.2. Cons.
3.2.1. When switching between desktops, desktop icons sometimes don't show up.
3.2.2. Launchpad is not as useful as it seems, you could always use spotlight or third-party search apps to find things quickly.