In this paper we examine how to efficiently build a brokers overlay to implement publish/subscribe in a wireless sensor network, trying to reduce sensor nodes energy consumption, memory required for buffering packets and delivery time. We evaluate, on the connectivity graph that represents the network, the performance of various criteria that can be used to select brokers among the set of nodes. We compare a dominating set approach with the selection of the best ranked brokers based on centrality measures. We finally give hints on how to implement a distributed algorithm to approximate the most efficient overlays.