It just depends on taste. KDE looks like windows, maybe thats why it's prefered by beginners.
http://en.wikipedia.org/wiki/Desktop_environment
http://en.wikipedia.org/wiki/Window_manager
Gnome and KDE are desktop enviroments, full of things you could need. File manager, calender, sound server, image viewer, a set of basic programs, own desktop games, icons, themes, login manager, ......
But most of this things are useless for me and I prefer to use KDE file manager and Gnome Texteditor, also KDE's japanese learnings programs but Gnomes image viewer. I use the Enlightment sound server and login manager and I have no need for a office suite, 'cause I use Lyx/Latex.
That's why I choosed a light window manager like fluxbox or xfce. It comes with nothing, no programs, no usefull stuff ... but I can install whatever I want, take the best parts of other wm's and built my own desktop enviroment from the scratch, so to say it