Clockwise has the benefit of keeping you on the lake side of the road so you don't have to cross to get to scenic viewpoints and you'll have better views while continuing to ride. From a traffic standpoint I'd suggest starting quite early at the Nevada end of S. Lake Tahoe. That way you avoid the town traffic and hopefully get up and over the Emerald Bay climb before traffic picks up. You'll still hit some traffic in Tahoe City, but that's usually not too bad.