It depends on who the stakeholders are. When you identify the stakeholders and their understanding about the proposed system ,then you can select the prototype or interface to validate the requirements. For example EUI prototyping is a low fidelity approach and it provides general idea behind the UI but not its exact details. Another one is end-to-end EUC prototype approach which /capture requirements from users (1) as textual natural language. These are translated to a list of abstract interactions (essential requirements) using an essential interaction library (2). These abstract interactions are transformed to an EUC model (3) capturing the sequence and interactions of a requirement. REs can validate requirements consistency between the various models and also against known, valid patterns of both Essential interactions(you can see :"Generating essential user interface prototypes to validate requirements") paper