I'm not an adcom but I can tell you right now that there is one obvious answer which will serve you very well:
You need to do some of all of the above but BY FAR the best thing you can do for your application is engage yourself in an activity that is truly organic and meaningful to you. If research is your bag, do that. If you can find a volunteering gig that really turns your crank, throw yourself into it. Make sure that you have enough volunteering/clinical experience/shadowing hours to assure adcoms that you are a community-minded applicant who knows what medicine really looks like and still wants to do it. But beyond that, realize that adcoms are looking for real human beings with genuine interests who are applying having engaged in something that matters to them. An application put together to tick the right boxes is not only obvious but also boring and a bit alarming. Go be a real person and apply when you have something interesting to say about yourself and your place in the world, and you'll be far better off, I promise.