I just got a principiante license a few weeks ago in CABA. I had gotten my US license apostilled. I had not gotten it translated and legalized here but at the Roca office they told me that it wouldn't have mattered because licenses from the States (and the lack of accompanying documents) give no info about what kind of license it is nor about how long you've been driving. I was told that my license could be for a tractor. It says class c on my US license but I guess they can't use the internet and look it up. Ridiculous, I know. I gave up and opted for the principiante license which does not let you drive on any road that has a speed limit over seventy for six months and no alcohol for two years.
Concerning the written test, it was not what I expected. The Spanish was not a problem but most of the questions had nothing to do with what was in the online course they make you take. I have heard that it's a much harder test than it used to be. I felt like I was floundering throughout test, never sure how I was doing, but I ended up scoring a 93,3. I do think a lot of the answers are common sense.
What I was told there was that if you have residency here, you need an Argentine license. I was stopped using my US license in the city last year. The officer asked her colleague and he said for me to go on, but I think that was only because of the pandemic.