Güerrín, at Corrientes 1368, was founded in 1932 by Italian Franco Malvezzi.
After arriving in Argentina in 1927 he wanted to open a pizzeria, and that he did.
Güerrín has been at this location ever since and is iconic. In recent years they even expanded into the space behind them and now the restaurant occupies the length of a city block.
Personally, I prefer the original dining room towards the front of the restaurant. The new dining space in the back is larger, though, and may feel more comfortable and spacious for families.
TIP: Visit at off-peak hours. Güerrín is everyone’s favorite and gets very crowded at peak lunch and dinner hours. For a more peaceful experience (especially if you want a slice at the bar), then be strategic and visit in calmer hours.