First of all, I've had the GP4000 (black) and the GP4000s and can't tell any difference whatsover between them. Buy whichever is cheaper.
I've used quite a few tires over the last few years, and the GP4000's are some of my favorites. Here's a quick run down on my take on various tires that stood out for various reasons:
Michelin Krylion Carbon - last a long time, roll well, decent grip most of the time, not very supple, even at relatively low pressure, downright scary lack of grip in cold (anything under 45 degrees or so), damp conditions. Good training tires most of the time. I only used these in a 23c size; the 25c size may take care of my lack of suppleness complaint. Longest lasting road tire I've used - I'd routinely get 4,000 miles out of the front tire and 2,500 - 3,000 miles out of the rear.
Conti GP4000 and GP4000s - Good all rounder. Don't last the longest, aren't the most supple, don't roll the best - but they're not far off the best I've tried in any of those categories. Puncture resistance has been pretty good for me - I wear out the tires before I get too many flats. I've used these in both 23 and 25c sizes, and prefer the larger version - a little more supple, seems to roll a bit easier. I get 2500 -3000 miles out of the front tire, 1500 -2000 miles out of the rear with these (I weigh about 220 and ride lots of rough roads).
Vittoria Open Corsa CXII (320tpi version) - sweet ride! supple and comfy, roll very well. Too bad they don't last very long. I get about 2/3 the tread life out of them as I get out of the GP4000. I used these in 25c size. Puncture resistance hasn't been bad, but I'd go broke if I tried to use these as my every day tire. Overall grip in corners when descending seems about on par with the GP4000's, although the suppleness of the Open Corsas is a great benefit for rider confidence on rough roads. They do seem to get cut up pretty easily - i don't let these anywhere near gravel or dirt roads.
I also used various budget Panaracers, Michelins, etc that were ok for the money but the tires above were the ones that stood out and were worth the premium.
JB