In recent years, attention has increasingly focused on enhancing user satisfaction with user interfaces, spanning both mobile applications and websites. One fundamental aspect of human-machine interaction is the concept of web usability. In order to assess web usability, the A/B testing technique enables the comparison of data between two designs. Expanding the scope of tests to include the designs being evaluated, in conjunction with the involvement of both real and fictional users, presents a challenge for which few online tools offer support. We propose a methodology for web usability evaluation based on user-centered approaches such as design thinking and linguistic decision-making, named Linguistic Decision-Making for Web Usability Evaluation. This engages people in role-playing scenarios and conducts a number of usability tests, including the widely recognized System Usability Scale. We incorporate the methodology into a decision support system based on A/B testing. We use real users in a case study to assess three Moodle platforms at the University of Guadalajara, Mexico.