Hi, i have installed KDE-based distros for over a year now, in a ton of PCs.
The thing is in each and every one of them, there was a problem (different problems on different hardware).
Mostly i had issues with the Sound speakers not being recognized by some of the PCs, or with the graphics card (which was a problem on almost
every PC i have it installed) or even with the wireless card.
So my question to you is : What is the perfect hardware combination so that, when I install KDE distros, there are no issues whatsoever?
(Especially with the graphics..)

there exists lists of tested/friendly Linux hardware and some distro's provide lists specific to themselves
ex:
http://www.linux-drivers.org/
https://wiki.ubuntu.com/HardwareSupport
http://community.linuxmint.com/hardware/search
and obviously Google is a good resource

if you don't prescribe/buy the hardware then maybe you should look at which distro supports the largest universe of hardware assuming the sw is your selection

another and probably easier way to address this is to determine what hw doesn't isn't supported

are these pc's new and old? newer can obviously be more problematic if drivers aren't yet available in the kenel or from the vendor - happened to me with a mb once and ended up running alpha distro release and it was heck