In this paper, two hybrid multi-hop/single-hop opportunistic transmission strategies with adaptive routing are investigated for prolonging the network lifetime of wireless sensor networks (WSNs). To achieve this goal, a systematic decision model that contains a network distribution block, a routing algorithm block, a traffic pattern block, and an optimal policy block is presented to determine the optimal transmission probability of each node. With packet transmission via adaptive shortest paths, two optimization strategies are proposed in the optimal policy block: A power efficiency optimization strategy and a power utilization optimization strategy. The power efficiency strategy aims to minimize the overall power consumption and the power utilization strategy endeavors to minimize the maximum power consumption among nodes. Computer simulations show that the power utilization strategy can achieve almost triple the network lifetime extension compared with the power efficiency strategy. Furthermore, the power utilization strategy is superior to the power efficiency strategy in terms of residual energy utilization for various network sizes.