For my IBM linux server, I started with RHEL and then moved to CentOS, the free clone. However, I finally gave up in frustration and installed Ubuntu Server; it has been running for a few years now with no problems. For my desktops, I tried many different distros and finally settled on Linux Mint, which is based on Ubuntu, but I like some of the refinements that Mint has made.
I own several books on unix and linux, including the "in a nutshell" series, Running Linux, and the "for dummies" series. However, in practice, I have learned mostly by doing and by the judicious use of Google.
In my work, I use Linux, Mac OS X, and Windows. OS X is my primary OS, but linux is by far the most fun. I tolerate Windows in order to be compatible with colleagues when needed.
For my desktop environment, I have tried many, including simple window managers. Overall, I prefer Xfce for its simplicity. Sometimes, I use KDE, because I use a triple-monitor setup and KDE provides the best features for managing desktops on multiple monitors. I still think that Gnome 2 was the most efficient desktop for my workflow. The closest to Gnome 2 now available are Gnome-Session-Flashback available via Ubuntu, and MATE, available via Mint and some other distros.
A great web site for comparing distros is DistroWatch.
Good luck and have fun!