If you need to install linux on a laptop, choose Ubuntu over the other derivations. There is simply more time and people working on the Gnome version of Ubuntu versus the KDE or Fluxbox derivations. When I installed Kubuntu 09.04 (Jaunty) things weren't "just working" like they do on my desktop. Having always preferred KDE to Gnome, I have never really tried the pure "Ubuntu" experience. I have to say, especially for laptops, the experience is radically different and ultimately superior.
I think I still prefer KDE over Gnome. If you still wanted the KDE experience on a laptop, I would recommend trying a distribution that is more focused on the KDE side (like OpenSUSE). For me, I prefer a Debian based distribution, though to be honest, it has been a while since I've tried OpenSUSE. Pure Ubuntu on this laptop has been a pleasure to use, so I'm going to stick with it -- though I now need to figure out how to customize and theme the hell out of it =)