I prefer Windows, because its the most common OS, and so its mostly used as platform for the good Games. Also its easy to use and if you know how (or why), something crashes, you can get Support for it, by just using Googles first Resultpage. The only bad thing about Windows is, that there are MANY useless Programs running in Background on "ready"-Mode, but that can be solved with a Batchfile in my Autostartfolder (at least on XP).
But if i really want to run a Server, then i would do it with an Unixderivate, like Linux, because who wants to reboot it several times, by using Windows?
P.S. Everytime i see a nonfruity and bitten Apple, i personally think: Ewwwww Apple!
Edit: Oh and who voted: "Don't vote for this, on pain of death"