Given an argumentation framework and a group of agents, the individuals may have divergent opinions on the status of the arguments. If the group needs to reach a common position on the argumentation framework, the question is how the individual evaluations can be mapped into a collective one. This problem has been recently investigated by Caminada and Pigozzi. In this paper, we investigate the behaviour of two of such operators from a social choice-theoretic point of view. In particular, we study under which conditions these operators are Pareto optimal and whether they are manipulable.