The train in Buenos Aires is clean and takes you pretty much anywhere on the grid for less than 2 pesos. It’s a great deal!
Cab’s are extremely cheap in the city and there's no real need to take the train, but for some reason I think hopping on the Metro is a good way to see the city's character. You get to interact with the people from there and see all types of new characters.
Argentinians call the train “El Subte” which comes from the word subterraneo (meaning subway).