I am Archlinux user for a long time and I think KDE works almost perfectly on this distro. Thought, I had not tried KDE on any other operating systems so that is why I ask: what is the unix system (both linux and bsd) that provides better support for KDE software? By "better support" I mean good compatibility and efficiency in user expirience (_id est_, speed!).

Thanks in advance for your answers!

not a very original question especially since users are biased to what they use. Have you tried Google'ing? If what you have works "perfectly" then why change?

I would think some think something like gentoo which is compiled by the user would provide the fastest implementation as it could be customized to your needs and system. The site http://www.phoronix.com does a lot of benchmarking

I use openSuse I and of course think it's the best and in reality it does provide multiple versions of kde4 from the stable to the bleeding edge, has a large set of repositories and a large user community. It also is a major supporter of KDE (and Gnome) and provides a good implementation of KDE. Others might disagree.

As the cost of Linux is free you can install virtualization sw (virtualbox, vmware, etc ........) and test out various distros without messing up your current system. Distrowatch.com is a good place to learn about what's available and their comments section can be both informative and amusing.

relevant readings:
viewtopic.php?f=63&t=6673&p=148593&hilit=%22best+kde4%22#p148593
http://thelinuxexperiment.com/guinea-pi ... tribution/
http://ubuntuforums.org/showthread.php?t=686630&page=2
http://wlnelson.blogspot.com/2009/06/fi ... ution.html
etc ...................