I'm not sure you've asked the question that you wanted to ask. That said, if you did know exactly what you wanted to specialize in, I would recommend shadowing in other specialties if you haven't done so already to solidify that preexisting desire.
I mean... if you literally just wanted to see physician/patient interaction, of course it does not matter which specialty among those that involve patient interaction you chose.
I am shadowing in Pediatric Oncology. It's great exposure to doc/patient interaction, as well as how nurses, doctors, psychologists, neuropsychologists, etc. co-exist within the hospital. They really do work collectively as a team to make sure that each child is getting all of their needs met.
Hope this helps. I think what you were asking was, are some specialities "better," generally speaking. Shadowing doesn't alway have to be so passive. Research, projects, and other opportunities can arise. Do not think of it as merely standing over a doctors shoulder. If that was the case, maybe it wouldn't matter what was going on in front of the doctor.