A C Zoom

The subway is called Subte and it is very good - roads can get into very bad traffic jams, so if subte is a possibility, go for it - buy the 10 ride pass for AR$9 [2008]
Also - be very careful to pick the right street entrance and the right turnstile to enter the subway. You must choose the correct one because once inside, you can only take the train in one direction. Very few stations have access to both directions, so if you make a mistake, have to pay for another ride to cross over and use the other turnstile or keep going until you come to a station that has access to both directions. Some subway maps identify the stations that have access to platforms in both directions - there will be a horizontal bar in the circle representing a station, but not all maps offer this legend.

While the subway is the best choice where possible, the subway does not have a wide-spread network which explains the heavy use of black-smoke spewing diesel buses on the streets! The heat in the stations and the trains can also get stifling but this is an issue only in January and February.