Argentina I hear is reasonably safe, though there are problems with petty crime, which shouldn't affect you as long as you are alert to your surroundings.

Colombia on the other hand isn't safe. There is a high threat from terrorism, there has been civil war there for over 40 years now, and criminal violence is a serious problem there, as well as the risk of being kidnapped in the Amazon regions. If you must go, be very damn careful.