i have used both phones, and can say that they both have different features which they are good at.
personally i found the camera quality to be the same on both, but marginally better on the samsung.
For multimedia purposes, the k850i is better, such as the music player and good reception radio.
I think that the G600 looks better than the k850i and feels much better when held. It has a good weight to it and doesnt feel cheap. k850i feels more plasticky and the buttons does not appeal to me.
Another point is the expandable memory, the microsd cards are slightly than the m2 card required by the k850i.
depending on what you are going to using the phone for most, you may prefer either of the phone. But as a general phone for everyday use with good build quality i would go for the G600.
hope it helps