i rode the 04 suzuki GSX-R600, R6, and ZX-6R before making my purchase.
the Suzuki was nice, but the styling was just too far out of whack for me. I liked the inverted forks (reminded me of my GSX-R750) and the power of radially mounted brakes.
the R6 felt OLD after riding the Gixxer6. it was like riding a Yamaha of yore... everyone went through a significant redesign while Yamaha sat on their laurels and only worked on the R1. I will say the seat was nice and comfortable, and the clipons were in a nice, comfortable sport touring position. I just didn't feel like I was getting enough for the money.
the Kawasaki stunned me with it's good looks... something Kawi's have lacked since the mid-90's 7R's and 7RR's. I had never owned a Kawi before, much less ridden one til that day. The bike was nimble on its toes like the Gixxer6. The front end was solid, duplicating the features of the Gixxer6. the suspension was a bit rough, as the back end tends to bounce over the bumps despite my 175lb frame. the bike was as light or lighter than the others, making it feel very responsive.
eventually, i had it down to the Gixxer6 or the ZX-6R... i went with the Kawi due to styling preference. I wanted a solid color and I wasn't a fan of the new stacked headlamps on the Suzi. after a few adjustments to the suspension, the ZX-6R feels every bit as controlled as the Suzi did, but also does it for a few hundred less than I could get for the Suzi.