Do the one you enjoy more and are more likely to do well in.
For information, and from a personal POV, RS is held in (may be surprisingly) high regard at some medical schools. Certainly in the East End of London an A2 or AS in RS would have been far, far more helpful for medicine practically than an A2 in physics. I would have thought it would be similar in any major conurbation.
The *only* real reason I can see for taking physics over RS is that you're interested in medical imaging, clin onc, anaesthetics or ITU medicine, and even there, I've not yet struggled with the concepts taught to us as medical students.