What Operating System for a server?

I'd like to run a little home server,but i have NO clue what operating system would probably be better for this. You get Windows Server 2000,2003,2008 (Which one?!) which is probably going to cost me money unless i torrent,or you've got Ubuntu server which i've never tried either - or regular Ubuntu. - which are Free,I'm primarily a Windows user - i DO use Linux Ubuntu sometimes,,but more accustomed to Windows. Remember this server isn't...huge and isn't going to host bloody Google.com,but i'd like to just set it up to host a small website. What's best? feel free to ask any questions and thanks