This paper presents a resource-aware and link quality based (RLQ) routing metric to address energy limitations, link quality variations, and node heterogeneities in wireless sensor and actor networks (WSANs). The RLQ metric is a combined link cost metric, which is based on both energy efficiency and link quality statistics. The primary objective of the proposed metric is to adapt to varying wireless channel conditions, while exploiting the heterogeneous capabilities in WSANs. Different from most of the existing simulation based studies, this research effort is guided by extensive field experiments of link quality dynamics at various locations over a long period of time using recent sensor platforms, which realistically addresses the real-world wireless communication challenges in WSANs. Performance evaluations, via test-bed experiments, show that the RLQ routing metric achieves high performance in terms of packet reception rate, network throughput and network lifetime.