The beauty of Ubuntu Linux is that it is easy to have more than one GUI (desktop) at a time. The underlying Linux OS is the same whether you use Ubuntu, Kubuntu or Xubuntu. This also means that software from each flavor will work on the others, only the interface changes.
Anyway, I wanted to try KDE GUI on my Ubuntu installation on my old laptop and found these instructions which still work for Ubuntu 14.04 LTS:
http://www.psychocats.net/ubuntu/kde
Really it could not be easier, and you get to select your desktop whenever you login to the computer.
KDE:
What I'm finding is it is very Windows-like. Not an exact clone but if you are used to finding your way around Windows you won't feel out of place for long with the KDE desktop.
I don't use KDE on a regular basis but I've always liked it. Whenever I'm trying to get people to make the jump to Linux I introduce them to KDE. Kubuntu is a great combination for most situations.