For KDE desktops IMO only OPENSUSE is probably worth while these days -- it's concentrating more than anyone else on KDE and it does work really well. Linux Mint does a passable KDE desktop too -- but most Linux Mint users don't really use KDE a lot and it's still essentially a "Bolt on" for other Distros than OPENSUSE.
OPENSUSE with KDE has the whole package nicely integrated -- what also is good about OPENSUSE's implementation is that if you do need any applications that say come originally from the GNOME desktop (GPARTED for example) they work seamlessly on the KDE desktop without needing the entire GNOME / other desktop interface to be installed either.
I'm not saying KDE is the best desktop -- for Windows users it's probably the most "Windows like" although as with all Linux distros you can do a lot of customisation.
If you DO want KDE then I suggest using OPENSUSE - the only downside is that it's an RPM based distro but package installation on pretty well all Linuxes is a lot better now and if you are used to apt -get type of commands OPENSUSE now has the equivalent - called ZYPPER - almost identical.
(OPENSUSE supports UEFI if you want it and of course a 64 bit system as well as 32 but systems -- and it's easy to create a bootable external device so you don't have to change anything on your internal HDD or muck about with boot menus).
BTW Here's my post on creating a Portable Windows 7 system (or any version of Windows) using OPENSUSE 13.1 KDE.