Various modeling approaches have been introduced to manage process diversity in a business context. For practitioners, it is difficult to select an approach suitable for the needs and limitations of their organization due to the limited number of examples and guidelines. In this paper, we report on an action research study to perform a comparative process variant modeling application in a process management consultancy company. This company experienced difficulties in maintaining and reusing process definitions of their customers. We describe how the requirements were determined and led to the selection of two specific approaches, the Decomposition Driven Method and the Provop approach. We comparatively evaluated the suitability of these approaches to develop variant models for six software project management processes of five customers. This study contributes to the field by presenting an industrial case for process variant modeling, reporting in-depth, real-life applications of two approaches, applying the approaches for hierarchical processes, and presenting guidelines for choosing an approach under comparable conditions.