CV Joints are "Constant Velocity" whereas Universal joints are not and they (U-Joints) will introduce a dynamic vibration into the driveline if not phased properly or at an acute angle..
There's an excellent article on Wikipedia about the CV joint;
Constant-velocity joint - Wikipedia, the free encyclopedia
VS. Universal joint
Overall - even when not running at a large angle - the CV joint is smoother and capable of carrying far more torque for a longer period when run at an angle..