I've used among others, Ubuntu, Fedora, FreeBSD, Madriva, Debian, Slackware, and CentOS. By far the most stable of the Linux distro's I've used so far has got to be CentOS hands down. I program for a living so i may put things to a harder test than most, maybe not, either way its just my opinion. Which distro is the best? Honestly, its the one you're most comfortable with and allows you to get the most accomplished without getting in the way.