MS1, here. TL;DR do more research. However, it depends on your goals.
The short answer is that the more research capability you have, the more you can contribute as a first-year, and the more likely you will match well and into highly competitive specialties. Schools see research as prestigious. If you have a first-author publication in mouse model gene up-regulation following circadian disruption, or whatever, you are not only demonstrating academic prowess but showing them that you are capable of working with accomplished faculty, that they trust you, and that your commitment to the publishing and revision process will likely translate to medical school at the highest level.
My BEST advice, though, is to do more in a field you wish to pursue. When you apply to medical school, and they ask Why Medicine, your activities should tell a story: what brought you to the field? You can't possibly want to go into all fields at once, surgical and non-surgical, inpatient and outpatient, general and specialty, longitudinal and EM. If you are interested at this point in med-peds, then perhaps becoming a CNA on an inpatient peds unit will tell the story on your AMCAS that you are excited about medical school for that specific career. If you want to work in neurology, reach out to your school's department to do more EEG research (just an example), and explain that your experience with brain research boosted your interest in studying neuronal pathologies. Let your interests guide how you spend your time, and you will find that answering "why xyz" feels much more natural.
This is all just my opinion from experience and NOT a fact/representation of my school.
