Both disciplines are totally different from each other and in principle, none of them is better than the other. In fact, both tend to have their own unique challenges, its own areas of research, and own topics of interest. Whether one chose botany or zoology would completely depend on the individual himself/herself and on his/her primary interests.
Those people who do not carry significant interest in either of these fields might find them quite dry and boring. On the other hand, those who love these areas of science can do great in either of those. In principle, both are different and cannot be compared.