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Research would strengthen your application for the med school application process.
As would an MPH. Also an MPH would strengthen your application for residencies, who will not care in any way about your undergraduate research experience.
OP, my advice is not to structure your life around what looks best to medical schols. If you have an interest in epidemilogy, infectious diseases, or healthcare management get an MPH. If you think you might one day want to be a researcher do research. If you don't want either and are just trying to game the game do neither and do something you are interested in instead.