No one is ever going to entirely agree on a “safest cities” list.
First of all, it’s hard to get a read on these things. Official crime statistics simply can’t be trusted in Latin America. I raise my eyebrows in amusement when journalists claim that Mexico City has a lower murder rate than cities like Washington D.C or Boston, erroneously assuming that Mexican law enforcement agencies report murder rates with the same accuracy as American law enforcement agencies. Also, many people in Central and South America don’t bother to report crimes such as robbery (or, in some cases, even murder) because they either don’t trust law enforcement, or they know that law enforcement is so inefficient that the perpetrators are unlikely to ever be caught anyway.
Second, personal experience tends to color perception.
I’ve compiled a list of what I believe to be the best cities for a tourist to visit in Latin America. The list is based on the criteria outlined on my cities guides, so you’ll want to click on the link to the city to get a thoroughgoing breakdown on the destination to find out why it ranked the way it did.