What countries in South America would be best to do medical work in?

I'm trying to get experience to get into med school and I would like to travel abroad to do medical work. Usually it's more hands on work, because they need all the help they can get and are more willing for you to try. Also, they don't have nearly the liability concerns the US does so I would be more able to try more. So, my question is what countries would be best for me to consider to those who have traveled? I don't necessarily want the worst 3rd world country, but I definitely don't want to go to a country that doesn't need the help. I'm also taking into consideration the terrain, because places like Chili, Peru, Brazil, and Argentina are amazing I just can't make an informed decision without experience. Thanks in advance!