I agree with what has already been said. If you are going to take this time to do research, in addition to your OPP fellowship, you want it to be adding to your curriculum vitae / ERAS application. Any research you do can count as a "research experience" on ERAS; however, research that produces publications, oral presentations, poster presentations, and abstracts will be far more valuable from an application standpoint. Research such as case reports, case series, narrative / scoping reviews, potentially systematic reviews, and retrospective reviews will be the highest yield for your experience as a medical student, because the timeline will fit nicely into that 1-year fellowship and allow you to produce something tangible. Prospective studies, benchwork, and RCT typically will not finish in that time. It is great to have experience with both, but if you want something tangible for your application, go with the first list. Of note as well, I would emphasize submitting abstracts to recognizable conferences in your desired specialty and preferably those where the accepted abstracts are not only a poster presentation, but are published as a peer-reviewed abstract within the journal associated with the sponsoring organization of the conference. Creating an abstract for a case report for a conference does not take super long, as long as you have guidance on what things may get accepted to that conference. Best of luck!