[Barnsnake]

You don't necessarily need to minimize the u-joint angles, but equalize them.
A U-joint is not a constant velovity joint when there is some angle in it. If you think of the engine running at a constant speed, the driveshaft is accelerating and decelerating, but averaging the same rotational speed as the tailshaft. A velocity graph for the driveshaft would look like a sine wave. If the two u-joints on the shaft have the same angle, and are in phase, the second u-joint applies the opposite acceleration and deceleration changes, so the pinion gear is now operationg at a constant rotational speed. If the u-joint angles are not equal, the system must accelerate and decelerate the rear wheels with each shaft revolution. It could also be that the rear wheels have enough traction on the pavement to force the engine's rotating assembly to accelerate and decelerate with each shaft revolution. Either condition will shake the hell out of the car.
If the differential is not rigidly attached, and can move some (perhaps mounted with rubber bushings), the pinion needs to be pointed slightly "down" to achieve equal angles when the pinion torques upward under load. Unfortunately this creates some driveline vibration under engine braking due to unequal angles.
Note that zero (or very near zero) u-joint angles will cause u-joint failure since the needles will never roll.