What kind of operating system would you run on your PC? One that hogs resources leaving you with just enough to do your work or one that ‘glides’ over the resources leaving almost everything for you to use?
I would certainly choose the latter. And if I ran a business, where a penny saved is a penny earned, I would be even more conservative about it.
I use Arch Linux with KDE Plasma on my main machine. This combination gives me a fully optimized base OS with a desktop environment (DE) that is known for being the most feature-rich.
However, I am always on the lookout for a DE that can run efficiently on less-powerful (aka less expensive) hardware, with an easy to manage OS.
So, in nutshell, I found Lubuntu 14.10 to be the best in performance among the Ubuntu distros. It offered me trouble free experience throughout my usage and I found it to be really stable. Anyone looking for a really really efficient distro and those with low powered machines can safely bet on Lubuntu 14.10
Based on my experience, I found Ubuntu GNOME to be the second best offering very decent performance with a very refined desktop environment. I thought Xubuntu would occupy this position but unfortunately, a bit of instability in the distro marred my experience. I would safely recommend Ubuntu GNOME 14.10 to users with modern laptop with or without touchscreen over the rest of the four distros.
As usual Kubuntu is the slowest of the lot and consumes the most power. You can expect the least battery life from Kubuntu. However, the desktop environment (specially the Plasma 5 upgrade) is mind blowing! Those with powerful modern machines and less usage of battery power can safely choose Kubuntu as it seemed to be the most exciting of the lot.
While FFmpeg has been absent from recent releases of Ubuntu Linux due to the switch over to Libav, with Ubuntu 15.04 it will return.
FFmpeg is back to being packaged inside Ubuntu 15.04 and version 2.4.3 is found within the Ubuntu Vivid universe archive as of yesterday. Libav forked from FFmpeg back in 2011. Libav was favored by the Debian multimedia team but there's been work for bringing FFmpeg back to Debian. FFmpeg/Libav are widely used audio/video codec libraries.
The FFmpeg details inside Ubuntu can be found via Launchpad.