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Best Server - For those saying RHEL/CENTOS, have you actually used it for a web server? It's too easy to hit rpm hell trying to get the latest version of some web framework or utility. I used to like FreeBSD for web servers but today you run into the same problem. So I guess I would pick Arch for pacman, bsd style init scripts and the minimalist approach. I honestly don't trust any distro for updates so I prefer the get latest and backup daily strategy.
Best Desktop - Arch inside a VM with Windows as the host.
Best Desktop for Newbs - Android tablet unless you hate people.
Runner Up - Clonezilla
I do run RHEL/CentOS as a webserver.