I've used 3 different tubies. Listed from worst to best...

Conti Competitions: Rubbish as a race tire. Hard compound was bouncing all over the place. Taking sharp corners, the rear would often give me that triple bounce. Great durability, though, and almost suffice as a training tire. They feel a lot like a clincher.

Conti GP4000S: Much better than the Competitions. If you mount your own tires, they seat really well and easily. Roll pretty smooth and definitely feel better than the clincher version. Fairly durable for a race tire.

Vittoria Corsa Evo CX 320tpi: Smoothest, best handling tire I've ever ridden by a HUGE margin. Feels like you're riding on a cloud, and they corner like they're on rails. Also the least durable tire I've ever ridden. I'm lucky to get a season out of them. But hey, if you're only using them for racing, I see little reason to go with anything else. If you race a lot of crits, I'd hesitate to ride the 21's as I had pedal clearance issues.