Software product lines engineering decreased the complexity of the development of products that share common features, and variability modeling helped define and manage the commonalities and differences between family products. That's why, through the years, many SPL languages have been proposed, tested, extended, experimented in case studies, and then developed even more. The proliferation of the modeling languages has made it difficult for engineers to select the appropriate one, depending on the domain context and on the user requirements. This paper first presents a panorama of the Software product line (SPL) modeling languages that have been proposed in the last two decades. A survey of few selected modeling languages is given in order to clarify their processes and the difference between the notations they use to specify requirements and to express commonality and variability. The article then provides software product line engineer with a guide that helps selecting the appropriate SPL modeling language, depending on the projects' constraints and requirements. The proposed practical guide is composed of a list of criteria that represent a basis for a comparative survey.