I thoroughly recommend Linux Mint 9 LTS and Linux Mint 10 Main Edition which are built upon Ubuntu 10.04 LTS (Long Term Support) and Ubuntu 10.10
Linux Mint 9 LTS Download
http://www.linuxmint.com/edition.php?id=52
Linux Mint 10 Download
http://www.linuxmint.com/edition.php?id=67
Linux Mint 9 LTS Release Notes/User Guide
http://www.linuxmint.com/rel_isadora.php
Linux Mint 10 Release Notes/User Guide
http://linuxmint.com/rel_julia.php
Also worth considering is Fusion Linux 14 which is a Fedora based distro.
http://distrowatch.com/table.php?distribution=fusion
Moving on to KDE I thoroughly recommend Linux Mint 10 KDE Edition
Linux Mint 10 KDE Download
http://www.linuxmint.com/edition.php?id=76
Linux Mint 10 KDE ReleaseNotes/User Guide
http://linuxmint.com/rel_julia_kde.php
Another KDE based distro. worth considering is Pardus Linux
http://distrowatch.com/table.php?distribution=pardus
LUg.