I'm going to state the obvious and say that the K3 handles a lot better. It's also faster, live view is better and the sensor resolution is better. But you could already tell that from the specs and reviews.. I think I do prefer the Fuji colors. It kind of resembles the old k20D which I never really got over, but I won't use that camera again, the inability to turn off LE NR is the killer. This setup is lighter and of course the lens is very much superior to anything you can find in Native K Mount. The dynamic range is much better than I expected too
If I was still a student I'd stay with Pentax but as a working person I think the Fuji suits my purposes better right now.