The main difference between a B.A. and B.S. is that in a Bachelor of Arts degreee, you are required to take more Liberal Arts/Humanities classes. In a Bachelor of Science degree, you are required to take more Science/Mathematics classes. It's strictly a personal preference.
That's not exactly true at Brown Thomas. You can complete an A.B. and still take mostly science classes. The only difference is in the number of courses you have to take for your major. The Sc.B. requires more courses (normally all of which are at a higher level than the courses required for the A.B.).