In Argentina I only have experience with Hertz (since at SLA [Salta] Hertz gives unlimited mileage while Avis had a severe mileage limit which would have cost me way more).

At Hertz, the single "super CDW" (or whatever they call it) covered both collision and theft (though it took a while to figure that out, since I had to talk on the phone to someone while at the Hertz office, since the people in the Hertz office didn't have good enough English to explain it me themselves!).

Also, see this thread about Avis accuracy regarding policies on rentals in other countries:

http://www.flyertalk.com/forum/avis/...t-country.html

After reading that thread, you may want to find the Avis Argentina website, see what it says, and then use Google Translate if you don't understand Spanish.