Win9x and WinXP have no real server versions, so why bother with either of them? Windows 2000 is showing its age. Windows 2003 is the only logical choice in my opinion.
EDIT: I did not vote because of the idiotic options. The first option is a crock and shows your inability to make an unbiased poll. The lack of Unix-based OSes is a big draw back, but I understand why you did not put them in the poll. My biggest complaint (the stupidity put into the first option was not the biggest, surprised?) is the fact there is no results button, so if I had wanted to choose something other than the plainly trollish first option, I cannot.