In answer to your question, first let me explain the difference between these streams, starting with

Botany

• Botany or plant Biology also known as plant science is the scientific study of plant life. Which one among the vital branches of biology, which deals with the study and Research related to plant life. Botany along with the study of plants also include the study of fungi and algae.
• The person who studies botany is known as botanist or a plant scientist.
• It deals with the study of plant structure, growth and differentiation, reproduction biochemistry and primary metabolism, chemical Products etc.

Zoology

• Zoology or animal Biology deals with the study of animal life like botany, even zoology is one among the vital branches of biology which further has its own sub branches.
• The person who studies zoology is called as zoologists or an animal scientist.
• Educe with wast studies related to animal structure, formation, psychological, evolutionary and systematic ethology.

Biomedical sciences

• It is a set of Applied Sciences applying portions of natural science or formal science knowledge, intervention or technology that are to be used in healthcare or public health.
• It combines the field of Biology and medicine in order to focus on the health of both animals and humans.
• As a biomedical science student you will study biochemical and physiological functions, anatomical and histological structures etc.

Now you need to understand is that, All the above three fields are very important and have a very good scope in future.

But all the streams are very different from each other as one deals in plants, other in animals and the third one in medicines so, firstly you need to evaluate what excites you the most was choosing botany will lead you into agriculture and that has a very good scope in future. Selecting zoology willing directly make you a doctor of animals. Opting for biomedical science will lead you into pharmacy and you know how composition some medicines are made and how medicines are useful for Healthcare.

See you need to evaluate your interest that in what particular field you be doing good because knowing what is best is temporary and building a career upon interest is permanent.

What is best among these three will not help you, but building a career based upon your interest will be the key to success.

My advice to you is, first know your interest and strength and based upon it choose your career wisely.

Hope this helps,