My least favorite in that wide range of dates is the 04-05 600 and thats based on looks alone, and they dont look bad at all its just my least favorite. I have a soft spot for the look of the 00-03 and 08+ is sexy. The only ones that would have an "issue" to look out for is the 06-08(and a few hear and there above) have issues with the R/Rs going bad but there has been recalls for most to help with that and even if not the replacement aftermarket parts are cheap and easy. There is also a brake MC recall for any of them after 04 I believe.
ALL GREAT bikes. Just take your time and pick the best one for you!
Also GREAT job progressing through your bikes. Good to see some one do it right. Would love to hear how you think it helped you as a rider.
K5 1K street - '10 600RR track