The deployment of onshore wind power involves spatial sustainability trade-offs, e.g., between the minimization of energy system costs, the mitigation of impacts on humans and biodiversity, and equity concerns. We analyze challenges arising for decision-making if wind power generation capacity has to be allocated spatially in the presence of such trade-offs. The analysis is based on a game developed for and played by stakeholders in Germany. The results of the game illustrate that there is no unanimously agreed ranking of sustainability criteria among the participating stakeholders. They disagreed not only on the weights of different criteria but also their definition and measurement. Group discussions further revealed that equity concerns mattered for spatial allocation. Yet, stakeholders used quite different concepts of equity. The results support the importance of transparent, multi-level and participatory approaches to take decisions on the spatial allocation of wind power generation capacity.