The difference between Ubuntu and Kubuntu?
I have said this before, but I dont mind repeating myself. The difference lies in the desktop environments. Ubuntu uses
Gnome and Kubuntu uses
KDE for their desktops.
Essentially this is the main difference (the other differences are the software written specifically for the chosen desktops), and is really a matter of personal preference and choice. Although if you install Ubuntu, you can always install KDE later and launch it from the login screen, and vice versa if you opt for Kubuntu you can install gnome.