I am currently using PCLinuxOS. I like it a lot. It is a nice desktop distro. It is RPM based, but uses apt and synaptic for package distribution. Overall, it is a stable OS with many nice features. I run it on an HP ZD7260US Laptop and everything (except for the Media Reader which works in no distro) just worked. The only hitch I had was getting VMWare Worstation and VMWare Remote Console running. If you are only using VMWare workstation the fix is easy, no so much for the remote console.
I have tried MEPIS and Ubuntu and didn't like either of them, I would recommend trying out PCLinuxOS AFTER the others, use it as your last one and I am sure that if you like KDE over GNOME (gnome is available but the default is KDE) then you will really like this distro.