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Server - CentOS + EPEL, never needed anything for servers that were not already there. Also, documentation for Red Hat RHEL is by far the best you can find.
For NAS I recommend openmediavault. The community is great and it is debian based so you are not locked on the cold when you need a bit of extras.
Workstation / desktop - Have tried Slackware (many, many years ago), CentOS, Fedora, Ubuntu, Mint and openSUSE. Settled with openSUSE for many reasons.
First I have to say, and some will throw rocks on me for that, that I like YAST. It is very handy to have a place to configure services, hardware and all on a desktop.
Second, the repositories of openSUSE are awesome, they allow you to try newer versions of some packages without disturbing the whole system, like a new version of KDE or gnome (extreme cases) or firefox and thunderbird (which they keep up-to-date). There are packages and updated packages for almost everything I wanted. I see it as compromise between rolling and version methods most distributions use. Disruption is something hated with passion on business.
Third, I like the new philosophy of "ship it when it is ready (or almost)". I skipped 12.1 and only now I am upgrading mine and client machines.
It is not perfect, of course, but is a very good system.
The only downside is that is way more difficult to convince a client to install linux on the desktop than used to be on XP and vista era. Even with all cost and headache (malware threats) on MS camp (I have to concede, Windows 7 is a very good system), people ask for Windows even when it does not make any sense. Lets hope WIndows 8 will unroll that.
obs.: I now that there is a classic mode for windows 8.