I am not sure how much difference there is between an MA and an MS. However, when it comes to my school, a b.s. does has a much heavier focus on math and science. For the BA at my school, you only need basic statistics but you have to take 4 years of foreign language. For the BS, you need basic stats, calculus, advanced stats, and 2 science labs (bio, chemistry, physics, etc) but no foreign language.
If you want to go to grad school, the BS seems to be the way to go. The BA students seem to fall pretty far behind by the time they get to the psychology research labs, at the end of the undergrad work. Most seem to have a lot of trouble understanding research methods and the stats involved.