I've used Windows most of my 18 years of life, starting with Windows 3.11 and ending with XP Pro. I've briefly used Vista and I absolutely hate it. It is a sorry excuse for an OS and M$ worst yet (even more so than Millennium Edition.)
2 years ago I switched to Linux and I haven't looked back. I currently use Ubuntu Gutsy on my PC, Xandros on my Asus Eee, and CentOS on my makeshift server. I'm currently in the process of setting up Gentoo on my newly built PC (well, personal workstation to be precise.)
... MacOS X (being a Unix-based OS) is pretty good too.