I have a 2002 R6 and my brother has a 2002 Gsxr 600. I have riden both and prefer the R6 (but im biased), we agree that the R6 is slightly quicker and easier to get leaning round corners. Having said that the R6's light front end, you can sometimes struggle to put the power down.
However I agree the suzuki gsxr600 is a great bike and there isnt much in it between the two.