One more to consider.
SimplyMEPIS 6.0beta2 Release is based on Ubuntu.
Beta2 provides an updated 2.6.15.6 kernel based on Ubuntu kernel version 
2.6.15-22.33.
http://www.mepis.org/node/9802
Mepis is staying with the KDE desktop.

Have tried Kubuntu 6.06 also.  I seem to like Mepis better.

Jerry