Straight or V

What is a better engine - a straight 8 or a V12?
Straight 8 is geometrically long, and is said to be vulnerable to torsional vibrations of crankshafts. But what makes the shaft more vulnerable - geometrical length, or a large number of crank throws?
Straight 8 is geometrically long, and is said to be vulnerable to torsional vibrations of crankshafts. But what makes the shaft more vulnerable - geometrical length, or a large number of crank throws?