I have an unabashed bias towards Continental. I won't even try to pretend otherwise

I am riding the GP4000s right now. I know it is a 23c tire, but the new "black Chili" compound and Vectran breaker give the tire great road feel, solid handling, good puncture resistance and it feels fast, fast, fast. I switched from the regular GP4000 and I actually can feel a difference.

I mentioned some in-house testing done by Continental before. Their results showed that a 23c tire was the fastest of all possible sizes (19c-28c). So if it is speed you're after, you might want to consider this factor.