It depends on which sector you are dealing with, Linux is by far the most popular among shared hosting follow by Windows where there are still plenty of demand for ASP and MSSQL.
we cant say that something is perfect.it varies from application to application.if you want user friendly graphics then windows are the best but if you want efficiency and performance then we can have linux and unix.so,none is best.
linux and apache are best for server systems, and also teh most popular ones too, while for personal use windows XP is better option as it has a better GUI and we have been using windows since we have been kids
For home and personal use, I prefer Windows 7 or Windows XP. Though Windows 7 first on the list as it is already been tested and approve by many, and is user-friendly.
Best Operating System is Linux because of powerful Security protection features . i would personally prefer Linux , But it is not easy for every user , people who know very well about the software can operate it .
When it comes for Server OS it's Linux CentOS which is most popular and widely used. Linux server are considered to be stable and secure comparatively. You can tighten server security at desirable level.