We spent about 3 weeks there in January this year through BA, Iguazu Falls & Mendoza. Wanted to do a bunch more (Bariloche & Patagonian region), but ran out of time.
It's a great place. The people are really friendly everywhere (even in BA, despite their reputation as being unfriendly) particularly if you attempt some Spanish, the food is great almost everywhere, and there's lots to do. It's an expansive country with a lot of diversity and generally long distances between key points of interest so you'll have to pick your spots.
- BA is a world-class city, we loved it and spent 10 days there (in an AirBnB in Palermo) - museums, restaurants, parks etc.
- Iguazu Falls is pretty spectacular, it's worth the trip up there. Better on the Arg rather than Brazilian side.
- Mendoza is the winery region, definitely worth a trip for a lazy few days in and around wineries.
- Your steak will likely arrive medium-well or well done if you don't specify "jugoso/a" ('juicy'), so be sure to mention that to the waiter. Don't get angry if the bill doesn't arrive at the table shortly after you ask - Argentinians like to loiter at tables post eating so it's customary.