While there are some MS programs in psychology, the field is traditionally more heavily associated with the MA. Ph.D. programs in psychology often prioritize research experience and theoretical understanding, areas that MA programs in psychology frequently emphasize more strongly than MS programs. MS programs in psychology might be more applied or focused on a specific area, potentially making them less suitable preparation for the research-intensive nature of a Ph.D.
Ultimately, the best choice depends on the *specific* MA and MS programs you're considering and their alignment with your research interests and career goals. Look at the curriculum, faculty research, and the track records of graduates going on to doctoral programs. Contact programs directly to discuss your aspirations and see if their master's degree would be a good fit for your Ph.D. ambitions.