I work in both environments: that is, whenever I think there’s a need for working in KDE or Gnome, I just logout and change session (I have both window managers installed). But that wouldn’t really answer the question, I guess.
Obviously, I really like KDE 4: it’s generally more streamlined than Gnome and while the new Plasma ‘paradigm’ was not really well received during launch, it has improved a lot. However, it’s still buggy, which is the reason, why I mostly login to Gnome. Gnome, is not without issues either: compared to KDE it’s visually less appealing and (from a user-perspective) less intuitive. At one time, I strictly logged into KDE because of Amarok: KDE’s music player is superior to the bunch of media players that come with Gnome.
So, for me the answer to the question ‘Gnome vs. KDE’ would be Gnome. We’ll see how the KDE team fares in the next (K)Ubuntu release.