Windows 2003 and Windows 7.
No matter what you linux users say, I'll always love windows.
I've never had any kind of trouble when it comes to it.
Reasons : (Some of them are personal)
-Most of my college applications were designed for windows and WILL NOT work on linux (Already tried using wine).
-User friendly, I'm kinda lazy and well, don't wanna waste my time installing stuff.
-Stability (If you're not a dumbass and know how to configure some stuff that WILL make your server unstable).
-When it comes to remote connections, windows has more options without installing any kind of stuff (Yeah right, putty takes less than 1mb, but at least from college, I'm not allowed to download stuff.
Suits me perfectly.
Well, these are some reasons why I prefer windows over linux.
Do not yell stuff at me if you really want me to use linux do not tell me reasons why I should do it, come to my country and gimme a full course.
Just my cents.