This paper addresses the problem of autonomous servoing an unmanned redundant aerial manipulator using computer vision. The over-actuation of the system is exploited by means of a hierarchical control law which allows to prioritize several tasks during flight. We propose a safety related primary task to avoid possible collisions. As a secondary task we present an uncalibrated image-based visual servo strategy to drive the arm end-effector to a desired position and orientation using a camera attached to it. In contrast to previous visual-servo approaches, a known value of camera focal length is not strictly required. To further improve flight behavior we hierarchically add one task to reduce dynamic effects by vertically aligning the arm center of gravity to the multirotor gravitational vector, and another one that keeps the arm close to a desired configuration of high manipulability and avoiding arm joint limits. The performance of the hierarchical control law, with and without activation of each of the tasks, is shown in simulations and in real experiments confirming the viability of such prioritized control scheme for aerial manipulation.