I race road and crits on tubulars. I've raced (just a couple) of time trials on clinchers. If I had to buy time trial equipment, I'd buy clinchers. I only race tubulars in road races and crits (now, though I've raced many seasons on clinchers) because the rear hub is substantially better than my quickly aging comparable clincher, they're 150-200 grams lighter than my similar clinchers, and the CRR is just a smidgeon better (reportedly).