The wife and I are going to do a mileage run/long weekend trip in September and need help deciding on what would be the best choice for such a short trip.

Background:

1. I need to net over 10k miles for this trip on American leaving from DFW
2. Neither of us has a preference over the three right now
3. One of our favorite things to do on vacation is enjoy local cuisine
4. We don't mind a strenous vacation such as having to hike around to see sites
5. We will be leaving on a Thursday and need to be back by Monday ready for work on Tuesday.
6. This won't be our last trip to any of these cities.

We have narrowed our choices down to Rio, Sao Paulo and Buenos Aires. Buenos Aires is about $100 more expensive to get to than Rio or SP.

For that short amount of time, which of these choices do you recommend?

Thanks!