SoCal

Worth it? Depends on you, of course. Very subjective. The exact number of stops can vary by airline, of course. You could fly to Sao Paulo non-stop from ORD on United (I didn't see with what airline your miles are). Not suggesting staying there for a week, but it's a quick hop to Rio on TAM (if you miles are with UA, TAM's in the Star Alliance so maybe you could use miles but, if not, the flight isn't expensive). I do know people who quite like Sao Paulo (for museums, restaurants, shopping, etc.), but I don't know it well at all, except for the airport. My wife (Brazilian) is not a fan.

I found Santiago a bit more modern, cleaner and perhaps safer than B.A., but also more expensive. Santiago definitely has historic charm, but I think B.a. has more. I'd regard both as safer than Rio, but if you'd be in the main tourist areas of Ipanema and Copacabana, and use tours and taxis when needed (the Metro system is pretty good), you'd likely survive (I did several times). Brazil is more expensive than Argentina. Not sure about Brazil vs. Chile. BTW, if you go to Argentina, don't refer to the Falklands, even in passing; they still strongly believe in "Las Malvinas" (same is true for other S.A. countries, but obvously less of an issue).

You have read up on both cities. If you go to the Lonely Planet Web site (the "Shop" section), you can buy and download individual chapters or their guide books. If I were going to choose a place to work or stay for a prolonged period, I'd probably choose Santiago (the area from Valparaiso, on the coast, to Santiago reminded me of Southern California), but for one week, probably B.A. (if you get bored-- which is unikely-- you could take a boat downriver to Monevideo). My favorite part of Argentina was Patagonia, but you don't have enough time to see both that and B.A.

Before you make a final decision, see if you can get to either place using miles. Having miles and being able to use them to go where you want, and when you want, can be different things. You may have to expand your list of possible cities. Now, if you have enough miles to fly Biz Class, that's the way to go!