I spend a fair amount of time in both cities.
Santiago is a fair sum safer than Buenos Aires, and increasingly so. But 5 nights in Santiago is a long time, and while you could combine it with a coastal trip, it is late winter and isn't exactly beachy. So, if you combined Santiago with something nearby, that is a good option. Any place a tourist is likely to stay and tour around is at least as safe as most parts of the US and Canada.
Buenos Aires is safe enough, and if you have the same street smarts you have in traveling around the big cities of Europe, you will most likely not encounter any bad experiences. That said, a tourist from France was just killed for resisting the theft of his camera in a public plaza. No piece of anything is worth your life. I go a few times a year and have yet to have a bad experience. For 5 days of a city experience, Buenos Aires is probably a better bet.
I like Santiago better (which puts me in the minority). I own a place in Buenos Aires, which I also like. I probably belong in therapy, which would be a
muy argentino thing to be
