Gnome and KDE are desktop environments, it's more of what you prefer, one is not better than the other. If you have an older computer with little RAM and a slow processor you might want to check out LXDE or XFCE. There are also distros that come with these desktop environments preinstalled like Xubuntu (XFCE) and Lubuntu (LXDE).
http://lubuntu.nethttp://xubuntu.orgEven if you use a specific desktop environment that doesn't mean you can't install applications from another, I use Gnome but also have KDE applications installed like K3B (burning software) and Kontact (contact manager).
A comparison of different desktop environments and some window managers.
http://en.wikipedia.org/wiki/Comparison_of_X_Window_System_desktop_environmentsYou can also try configuring your own desktop environment by installing an ubuntu's minimalist cd (which installs only base package and no gui) and then install everything you want through the command line.
https://help.ubuntu.com/community/Installation/MinimalCDhttps://help.ubuntu.com/community/Installation/LowMemorySystemsexample:
sudo aptitude install xorg fluxbox fluxconf gdm firefox thunar
This would install X (GUI), fluxbox (window manager), gdm(login manager), firefox (web browser), thunar (file manager)
You might also want to look into Linux from Scratch
http://www.linuxfromscratch.orgYes I know I kind of got off topic