To the best of my knowledge, in majority of the streams of B.Sc courses for life science candidates, definitely, there will be a combination of Botany and Zoology. So, you will have to go through both the subjects in Graduation with B.Sc.

As per the best choice between Botany and Zoology, you can choose the one as per your interest. Botany is purely related to Plants. All your study is related to various kinds of plants which belong to various families.

Zoology deals with the study of animals. You have to study various metabolic systems and metabolic processes of animals like

-Digestive systesm

-Respiratory system

-Reproductive system.

So, I suggest you to make the choice as per your interest.