My husband and I spent a month a few years ago driving around Argentina with friends. We were in Salta/Jujuy/Atacama for some two weeks. The only really bad road I remember was during a detour leaving Salta though a very poor area. The holes were huge and full of water so you didn't know how deep they were. The main road Salta-Purmamarca-Atacama was perfectly ok and traffic was very light in January, the road Purmamarca-Atacama was virtually empty.
I have only driven myself in the US once, Hamptons-Manhattan Sunday evening, not sure how typical of the US that is. It was way more stressful than Salta/Jujuy/Atacama. Compared to Europe, driving around in the more mountainous areas in Salta/Jujuy felt much easier than driving around in narrow and crowded Swiss/Italian/Austrian mountain roads. We did leave the paved roads quite a lot but although the non-paved ripio roads were bumpier I don't recall any difficulties. Not sure we would have ventured into some of those roads on our own though, as sometimes there was really no one around and none of us can change tyres.
So, I wouldn't hire a driver out of concern for the roads but I would definitely consider a combined driver/guide if I was new to Argentina and wanted to learn more about the region.
If you rent a car, my advice would be to rent a 4x4 unless you are planning to stay on the paved roads. To the advice already given I'd add read the weather reports. We were caught in a very heavy thunderstorm in the middle of nowhere and we had to stop and wait until it stopped hoping we wouldn't get struck by lightning. It is also wise to let your hotel know what you'll be doing during the day if you are venturing into deserted areas. Lastly, tell the rental company at the time you rent the car that you'll be driving into Chile so that they can fix the paperwork.