Active and Assisted Living (AAL) aims at providing services for elderly or disabled people in their homes using modern smart home technology and AAL software. The accessibility of user interfaces for such systems is of particular interest. This article proposes a model-based solution for selecting the best device and modality for user interactions of AAL services using the Ambient Assisted Living user interfaces (AALuis) framework. The best device and modality for a given situation depends on context information provided by the AAL system. An exemplary household was modeled as a Bayesian Network, incorporating a selection of devices and their modalities, together with relevant context information regarding the user and the environment. Each entity of the network is assigned with a probability. For devices and modalities these probabilities represent a measure of their suitability for output for the user, given the context. This model was then used to simulate different scenarios, in order to review the results of this selection mechanism.