I use both interchangeably. One is not better than the other. They are just
different. People like Gnome for its simplicity and KDE for its configurability.
I have not had a problem with KDE or Gnome on a stable Linux distro. In
experimental releases I have experienced problems with each.

The best thing to do is try them both out. You can install Kubuntu from Synaptic
or 'sudo apt-get install kubuntu-desktop' from a terminal. If you install
Kubuntu instead of KDE you get the same thing as if you installed Kubuntu from
the outset. It includes KDE plus all of the packages that Kubuntu team have
selected including: OpenOffice, Kontact, Konversation, amaroK, K3B, and more. If
you install KDE you will get: kde-amusements, kdeaccessibility, kdeaddons,
kdeadmin, kdeartwork,
kdegraphics, kdemultimedia, kdenetwork, kdepim, kdesdk, kdeutils,
kdewebdev, kdevelop3 and the kde-core metapackage. If you install just kde-core,
then you get the bare minimum to run KDE applications from Gnome. If you have
the hard drive space it is a good investment in time and effort to install both
to see which you prefer. Once you decide you can delete which ever you want or
keep them both around.

At some point in the installation process it will ask you to choose your desktop
manager. KDE used KDM and Gnome uses GDM. It does not make a difference as far
as I can tell which you select. Both KDM and GDM work with either window
manager.