Recent progress in model-robust designs has focused on maximizing estimation capacities. However, for a given design, two competing models may be both estimable and yet difficult or impossible to discriminate in the model selection procedure. In this paper, we propose several criteria for gauging the capability of a design for model discrimination. The criteria are then used to evaluate a class of 18-run orthogonal designs in terms of their model-discriminating capabilities. We demonstrate that designs having the same estimation capacity may differ considerably with respect to model-discrimination capabilities. The best designs according to the proposed model-discrimination criteria are obtained and tabulated for practical use.