Although the others are no slouches, DistroWatch links to TuxRadar for the best KDE Linux distro
:The verdict? The best KDE distribution today is openSUSE 11.2: "Our winner is openSUSE. It's a distribution that's got the professional sheen and gloss that only Novell can bring, and it's a distribution that always manages to bundle a cutting-edge KDE installation that will last you the full nine months of the distribution cycle. The custom artwork looks great, and shows that the packaging team has a great understanding of what KDE is capable of and what users need from their desktop. YaST is always going to be unwieldy, but its fantastic integration into the KDE desktop (it's written in Qt) makes Linux feel much closer to its Windows and OS X competitors than other KDE distributions.
It's also the most Microsoft-friendly of the distros since Microsoft partnered with Novell
back in 2006 for greatest document format compatibility and virtualization. (That's good or bad depending on how you look at it.)