Install Ubuntu or Kubuntu?

I want to upgrade my Ubuntu Lucid to Kubuntu Maverick (with a fresh install of course). I want to try KDE, but I have heard there are slight issues with the native Qt applications compared to the GTK application equivalents - such as nvidia-settings, Gimp, Ubuntu Software Centre, and especially th eSynaptic package manager (which in detail showed the administration package / KPackageKit is not powerful yet than synaptic)

I believe we can have run GTK+ applications in KDE, but GTK+ applications do not blend with the KDE desktop. Also Java does not provide a GUI for KDE/Qt.

Should I install Kubuntu (KDE/Qt) or stay with ubuntu (GNOME/GTK +)?

Using Ubuntu (Gnome-desktop) or Kubuntu (KDE-desktop) is in the end a choice of preference and maybe what applications you use more.

You can even install both, by making sure that both packages, ubuntu-desktop and kubuntu-desktop are installed. With this setup you can decide when you login, which desktop you want to use (or with the change user option have both desktops running at the same time).

if you want to have a better blend of GTK apps in KDE, you can select the Curve theme for them in the settings (I think it is in appearances in system-settings).

I do not think there is a real objective answer more than this for your question, and we do not want to start any flaming here :)

In addition do txwikinger answer, I can say that Ubuntu is Canonical's flagship product and it is polished more (for example: Software Center, UbuntuOne Client). So I would stick with Ubuntu, but install kubuntu-desktop package and try it yourself :)