The design of model transformations is a key aspect in model-driven development processes and is even more important when alternative transformations exist. The transformation designer must be able to identify which alternative transformations produce models with the desired quality attributes. This paper presents design guidelines for defining model transformations to deal with alternative transformations in which the selection of the alternatives is done based on quality attributes. The design guidelines are defined in the context of a multimodeling approach which, unlike conventional transformation processes that only use source models as input to apply transformations, also uses two additional models: a quality model for representing quality attributes, and a transformation model for representing the relationships among quality attributes and the alternative transformations in a particular domain.