As far as I know, Tuenti is your best bet. They're probably the cheapest provider and have everything pretty much automated. Just buy a SIM card (should be around ~1USD probably) in a kiosk or somewhere, follow instructions and you're almost set. You might even get one for free if you walk around long enough.
Afterwards you should top-up online, which will start a "combo". There's currently a "monthly" combo for $190 (~8USD) which will get you 2.5GiB to use in 30 days, plus 100 minutes (but who cares). There's also a "super monthly" for $290 which gets you 5GiB.
Coverage and speed are as good, if not better, than any other company. I use it daily, sometimes intensively, without any issue. It will also work in the entire country, but I don't think it works abroad, even in neighboring countries.
They used to have a list of places where you could get a SIM card in their website (https://www.tuenti.com.ar/solicita-chip-sim-gratis/puntos-retiro/) but it doesn't seem to be working. By asking in kiosks/minimarkets you should easily find one.
Hope you enjoy Buenos Aires. Be sure to visit the pizzerias.