Wow - I'm surprised Krita has been in development that long. It just qualitatively feels much more modern than GIMP. Maybe it's because I focus more on drawing making heavy use of the brush system which IMHO is significantly better in Krita.
I used to use both GIMP and Krita, but I switched over to Krita-only when many of GIMP's filters were bundled into the G'Mic plugin, which is now installed by default in new releases. You don't get everything but I'll trade it for the UI upgrade (and everything else) xD