You shouldn’t volunteer just to impress Ivy admissions or anyone else. It should be an activity that flows out of your interests, that you do because you love doing it.
For example, when my daughter was in 6th grade she started volunteering for a dog rescue group because she loves dogs. A couple of years later she started volunteering at a natural history museum staffing educational carts on science, because she loves science and that museum. She wound up volunteering at the museum for five years. That fit her interests. She also was taking lots of science classes in high school and now plans to major in science in college.
One of her friends volunteered several years at a hospital, but that’s because she plans to be a doctor. I know of another person who volunteered at a zoo during high school, because she plans to study wildlife in college. Do you get the idea?
If you can’t find or create volunteer opportunities related to your areas of interest for possible majors and careers, then go with what is most fun or meaningful for you, or perhaps where you can develop the most new skills and knowledge that could come in handy later. You should be getting something out of volunteering besides trying to impress others.
No amount of volunteering will gain you admission to an Ivy. It can bolster an application, but it’s usually clear to admissions officers if you’ve done something to pad your resume and application, or if you’ve done something because it flows from your interests or your joy of helping others. So there is no right or wrong choice between volunteering for Habitat for Humanity or the hospital (or somewhere else). Which activity interests you?