even for competitive fields, as long as you do meaningful research and be productive it'll look good..of course it'll help if you do it in the field you are interested in since it'll help with connections/networking ..when you do decide on a field I do recommend you get a side project just to show your interest and commitment to the the field but it is not required, especially at this stage if you're a M1. couple of friends got into neurosurgery at top programs and never did strictly neurosurgery research (one did vascular, ortho research, etc), another got into a top radiology program and did cardiovascular research..but all of them had productive research experiences (i.e. abstracts/publications)..there is research that combines fields like neuropthamology (how ever you spell optho) research (i.e. optic neuritis in multiple sclerosis, etc), spine research in ortho/neurosurg/rad-onc, ENT/neuro, vascular/neuro, etc...if you want to be on the safe side, do something that is relevant to many different fields, like cancer or immunology research (inflammation, autoimmune, infectious disease), etc---this will cover derm, rad onc, optho and ortho..or you can might as well choose a project in the most competitive fields (derm and optho) this way you can get a head start in research if you do end up sticking with that field or you can always change your mind later..