Fedora Core 4. But only because I am openly new at Linux and know nothing about it other than what has been posted in this community. Before getting into Linux I did a bit of research and found a strong pull toward Fedore Core as the most popular distro. This was not so much because it was better than anything else but it seems like there is a larger support base for it with various forums and sites dedicated to FC.
So my Linux development laptop runs FC4 and my dedicated server runs FC also.