Hello Khushi, there is no comparision between any two fields of engineering because all the sciences are required for humankind. Physiotherapy deals with the interaction of patients and helping them to maximize their health to full potential whereas  Biomedical engineering is a stream which is useful for going into pharmaceutical fields or research areas in medicinal fields. It is the integration of biology using engineering methods.

The decision lies based upon your interest.

Hope this helps.

Thank you.