I never worked more than 20 minutes continously on KDE, so recommending you GNOME will be much a biased answer.
Well, install both, work on both for a few days (Yes, I mean it, not a few hours, or it'll be too early to make a decision, like me), stick with the one which is comfortable to you.
Well, there is always a third, fourth, fifth... choices. Try Other WMs like XFCe, IceWM, Fluxbox, Enlightenment, etc too.