hehe tricky question, that of yours. :)
I hope not to start the classic distro battle here.

So I will only say that I think Mandriva config tools are very user friendly and the distro has excellent hardware detection. If you, like me, don't want to deal with manual changes to config files, I'd recommend it.
Mandriva has always had excellent KDE support (it's the default desktop).

Admitedly it's currently not the most popular distro, but to me it always has been the distro for the 'normal user'.

That said, there are a lot of other very good distros out there, of course.

I use Arch 64bit but build Kdenlive, MLT, frei0r and ffmpeg for myself. I do use neither KDE nor Gnome but some loose pieces of software with Openbox as window manager, works fine though.

Mandriva 32 bits (yes old school hardware here)

Ubuntu 32bit (gnome
10.04 Lucid Lynx

kde dependencies get installed with ease from cli apt-get/aptitude or gui driven synaptic when installing kdenlive.
Medibuntu repo allows for non-free stuff like libfaac, this arises due to some files in faac being under a non-free licence. To get ffmpeg enabled with x264 encoding support, you can use sanub's PPA as defined here: http://www.kdenlive.org/forum/kdenkive-078-packaged-ubuntu-maverick-lucid-karmic-jaunty