Future wireless communication systems require efficient and flexible baseband receivers. Meaningful efficiency metrics are key for design space exploration to quantify the algorithmic and the implementation complexity of a receiver. Most of the current established efficiency metrics are based on counting operations, thus neglecting important issues like data and storage complexity. In this paper we introduce suitable energy and area efficiency metrics which resolve the afore-mentioned disadvantages. These are decoded information bit per energy and throughput per area unit. Efficiency metrics are assessed by various implementations of turbo decoders, LDPC decoders and convolutional decoders. An exploration approach is presented, which permit an appropriate benchmarking of implementation efficiency, communications performance, and flexibility trade-offs. Two case studies demonstrate this approach and show that design space exploration should result in various efficiency evaluations rather than a single snapshot metric as done often in state-of-the-art approaches.