The IPv6 Routing Protocol for Low power and lossy networks (RPL) is appearing as an emerging IETF standard of Wireless Sensor Networks (WSNs). RPL constructs a Direct Acyclic Graph (DAG) according to an objective function that guides the routing based on some specified metric(s) and constraint(s). In the last decade, a number of RPL simulations have been proposed for several metrics and constraints, but for the best of our knowledge there is no comparative evaluation for RPL energy-aware routing metrics. In this paper, we present the first comparative study of RPL energy-aware routing metrics on Grid topology. Our experiments show that multi-criteria metrics perform better.