While choosing an engineering branch you should consider your career goals, interests and inclination. Both these branches have different scope and objectives. Mechanical engineering deals with designing and manufacturing mechanical systems, and Biotech combines Biology and Technology for development in areas like healthcare, agriculture, and environmental conservation. It is important for you to go through the curriculum of both these branches to decide which one better suits your interests and long term goals.

Mechanical will offer you job opportunities in the automotive, aerospace, energy, robotics, and manufacturing sector. After Biotech you can work in the Pharmaceutical, Healthcare, and agricultural sector. It is up to you to analyze the potential and market demand for both these branches. 

If you are skilled in Maths, Physics, Problem-solving, and Design, you can opt for Mechanical. On the other hand, Biotechnology requires an understanding of Biology, Genetics, Biochemistry, Lab Techniques, and Data Analysis. Biotechnology is constantly making new innovations in fields like genetic engineering, drug development, and bioprocessing.

This choice is highly subjective, and completely depends upon your own interest. Both these fields are making rapid progress in their own manner. You have to ultimately decide which one is more in line with your own aspirations.