KDE, because it's what all the cool guys seem to use 😃
I started off with Gnome because that's what Redhat defaults to but one of my friends said that he used KDE so I tried it. I found it very easy to customize and just generally got on with it. However, when I first came to Linux I was very scared and didn't want to change anything so I never really tried with Gnome ... hey ... I guess I've never really tried Gnome then.
/bubble scuttles off to give Gnome a proper try out
[edit]
KDE, Gnome sucks (well I do to be more accurate), I can't figure out how to change the desktop, not like you can with KDE's Control Centre
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