For most students planning on pursuing further education in zoology (like a master's or PhD), or aiming for a career directly applying scientific knowledge (research, wildlife management etc.), a BS is usually the preferred choice. The stronger science foundation is better preparation for graduate-level coursework and research.
However, if a student is interested in a career that blends zoology with other fields, like science communication, zoo education, or environmental policy, a BA might offer a broader skill set by incorporating courses in writing, communication, or social sciences.
Ultimately, the "better" degree depends on the individual's career aspirations and academic preferences. Consider carefully what you want to do after graduation and choose the degree path that best supports those goals. Examine the specific curriculum of each degree program offered by the university you're considering as they can vary significantly.