To me asking which one is better is like asking which woman is better a thick woman or a slim woman. They are just different and I like them all. I find 600's to be more fun in the corners and 1000's to be more fun on the straights. I hate hearing people say that there is no skills with going straight, all you are doing is twisting the throttle. With a 600, at the end of the straights you're going like 140/150 mph and on a 1000 you're going like 160/170 mph. With the 1000 if you do not chicken out by braking early, coming to that corner with those speed really get the heart pumping and honestly, I find that is where I do most of my passing since a lot of people are scared to brake late. Plus with the 1000, even going straight you need good throttle control because in the lower gears wheelies can surprise you and kill drive; that wheelie surprise never happens to me on a 600. On the street, the 1000 feels safer because I have instant monster power at any given moment so if danger is around, I can get away from it, with what feels like instant power/speed. While on the 600 you have to be in the right gear and power range (the whole build up power thing).
If I could only have one bike to do all type of riding, I would go with my 1000. If I was only able to ride track then I would keep the 600. I find it more fun beating up on people at the track with a 600 rather then a 1000. When you beat up on people with 1000's they say, "Well it's a 1000." When you beat up on people with a 600 they shut the f@&k up and walk away.