This paper describes a comparative analysis of alternative methods of constructing composite indicators to measure the sustainability of the agricultural sector. The three methods employed were Principal Component Analysis, the Analytic Hierarchy Process and a Multi-Criteria technique. The comparison focused on the irrigated agriculture of the Duero basin in Spain as a case study, using a dataset of indicators previously calculated for various farm types and policy scenarios. The results enabled us to establish a hierarchy of preferred policy scenarios on the basis of the level of sustainability achieved, and show that the most recent CAP reform is the most sustainable agricultural policy scenario. By analyzing the heterogeneity of different farms types in each scenario, we can also determine the main features of the most sustainable farms in each case. The analysis demonstrates that full-time farmers with small to medium-sized farms and sowing profitable crops are the most sustainable farm types in all the policy scenarios. All of this information is useful for the support of agricultural policy design and its implementation, as we attempt to improve the sustainability of this sector.