Pros: The largest library of programs and applications. Some commercial games work only with Windows and DirectX. Almost all hardware has drivers which are compatible with Windows. Most widely used.
Cons: Prone to viruses, spyware, and adware if proper steps not taken such as installation of internet security software, which reduces performance speed. Requires regular maintenance to avoid system errors and reduced performance. Even with maintenance, issues can slowly accumulate requiring a re-installation of Windows to restore performance and fix software issues. Purchasing a Windows license/install disk can be relatively expensive Windows Vista, the most recent version of Windows, has high system requirements.
Pro: 1) No need to worry about viruses or adware. 2) Nice suite of integrated applications (iLife). 3) Nicely designed hardware. 4) Shareware applications tend to be better designed. 5) An intelligently designed OS (adding a network laser printer is a breeze).
Cons: 1) Accessories tend to be more expensive (hello TV tuners!). 2) Not compatible with a LOT of PC hardware. 3) Safari & FireFox on Mac don't work for all websites. 4) Command key is in an awkward position. Control key on Windows makes more sense. 5) Some software just not available on Mac (hello MSN Messenger with video).
pros: open source, stability, variety, thousands of apps for everything imaginable, constant updating and improvement, etc.
Con - you have to learn about computers and the os to install and maintain it correctly.
Focus on window 7