To date, the assessment of the technical level of individual elements of hydraulic drive systems has been significantly addressed, but most of them were positive-displacement machines. Thus, the development of a criterion which takes into account the maximum number of indicators and hydraulic devices and is based on common methodological principles is an important scientific and technical task for the assessment of the technical level of hydraulic machines, hydraulic units, and hydraulic devices. Based on a systematic analysis of the technical level evaluation indicators of a wide range of hydraulic drive system elements, namely hydraulic machines, hydraulic units, and hydraulic devices, a definitive criterion for assessing their technical level is synthesized. There were two stages in the study: theoretical and experimental. Initially, the most important factors influencing the reliability and efficiency of hydraulic devices were defined on the basis of operations research methods (hierarchy analysis method and multicriteria optimization). After the synthesis of the criterion, an experimental test was carried out based on a comparison of maintenance costs of real hydraulic devices. The obtained criterion allows one to make an assessment depending on constructive and operational indicators, based on common methodological principles. A comparison of the characteristics of maintenance costs of hydraulic devices per unit of power was made. Characteristic curves are hyperbolic, which proves the validity of the criterion.