Slackware default install with KDE
I personally would recommend some careful reading, experimentation on a test machine, and adoption of Slackware full install with KDE as desktop environment. This is assuming that readers of this particular forum have problem-solving abilities, a general background of IT skills, and curiosity. You can add package management, compile from source, and/or download binaries. It is remarkably difficult to break Slackware. I've tried.
What you get is what upstream pushed out. With choices, e.g. OpenOffice and LibreOffice installed and functional along with the default Calligra.
Some other observations on the OA follow...
"If you're going to use GNOME, right now, not having seen what Ubuntu is going to end up doing, I suggest trying it via Fedora."
Fedora Workstation is very nice, but the Korora Project makes it nicer with the Arc theme, a 'traditional' overlay on Gnome (Windows 7 work-alike), multimedia codecs/software installed, and a range of applications. Chapeau Linux is another 'batteries included' Fedora flavour that has less radical tweaking of the Gnome desktop.
"If you just click your way through the Debian installer you'll end up with a GNOME desktop, which offers a decent experience, but I find Xfce more suited to Debian."
Debian installer tasksel will provide a choice of desktops at the 'select software' stage. You can select more than one. Debian is also the only distro to allow offline installation of a YUGEtm range of software.
Finally OpenBSD. Just saying.
PINT: to all those involved with this outrageous, distributed, self organising, wonderful, argumentative, opinionated mud-ball of a project of totally free and unencumbered software. I clearly recollect the day I downloaded a live Ubuntu iso, burned it, and tried it out. Amazing. Thanks Mark, Pat and all.