I have been using various distributions since I came in contact with Linux in 1999 when I started studying computer science at the University of Technology Chemnitz. For the most time I have been using Debian in one way or another and tried to give back by doing some packaging work. Although I never found the time to jump through all the hoops and red tape to become a Debian maintainer.
Fedora, and by that CentOS as well, became the choice for the desktop and correspondingly for servers when I started my first job after university at Raritan.
Arch is something different. I haven't used it on my desktop or a production system. But it allows me to take a look at a something else beside deb and rpm based systems and it is nice if you want to play with bleeding edge stuff.