What is the best operating system?

Mac OS X 10.0 was a radical departure from the previous "classic" Macintosh operating system. Mac OS X was Apple's answer to the long awaited call for a next generation Macintosh operating system. Mac OS X 10.0 introduced a brand new code base, completely separate from Mac OS 9's code base, and all other previous Apple operating systems. Mac OS X introduced a new Darwin Unix-like core, as well as introducing a totally new system of memory management. Mac OS X is widely regarded to be the best operating system Apple has ever produced; however, Mac OS X 10.0 was a rocky start to the Mac OS X line, plagued with missing features and performance issues -- although it was praised for being a good start to a brand new operating system in terms of completeness and overall operating system stability.