BA and Rio - where to start/end the trip?
 

We are going to Rio, BA and Iguazu Falls (possibly Salta in the middle). We were wondering if it's better to start in Rio and end in BA, which might feel a little more comfy / luxurious. Or start in BA and end in Rio, with the beaches. Does anyone have any recommendations ?

Whatever order you choose, make sure you stay in Recoleta area of Buenos Aires where it is safe. We moved there from a hotel in the city center and it was basically unsafe.
Your start and end locations should be dependent on the best flights to and from BA or RIo.

Either way would work fine but if you want beaches at the end then BA to Rio is the obvious choice. I haven't been to Rio so can't comment but we do like BA and have spent quite a lot of time there. As suggested above, Recoleta is a nice upmarket area but I would also take a look at Palermo (we like Palermo Soho). San Telmo is fun and quaint and great for budget accommodation but I wouldn't stay there as it can be a bit iffy at night.

I would highly recommend hiring a car to explore Salta and the Northwest - you could see a lot of great stuff in 3 -4 nights but a week would bet better . You could fly from there to Iguazu, explore the Argentine side of the fall on arrival and then cross to the Brazilian side , explore the falls there and then fly to Rio from For de Iguazu.

I had no unsavory incidents when I was in BA this past December, even though I stayed my final night at the edge of the slightly sketchy area near the infamous Florida Street. Palermo covers a wide range of neighborhoods of varying quality. I didn't care for my Palermo location the first time I visited BA, so switched to Recoleta for my first nights, and had one night at the end elsewhere because I thought I wanted to visit the Reserva Ecologica Costanera Sur.

If you can figure out what you want to do in Buenos Aires, I would look for a hotel nearby and just use taxis if you are worried about late night activities.

I haven't been to Rio either, I would see how flights lay out to decide. Be aware that there are two airports in Buenos Aires, also.