Taking a taxi in Buenos Aires is as easy as taking a taxi in any other city.
Official taxis are painted black and yellow and they always have a sticker on the front door with the license code of the taxi.
I highly recommend taking radio taxis rather than standard taxis since you can easily trace these taxis in case something happens or you lose an item. Radio taxis have a rooftop sign indicating that they are radio taxis.
Another reason you should take radio taxis is that radio taxis are metered and in most cases the meters are functional.
How to hail a radio taxi
You can either call or flag the taxi down with your hand
In Buenos Aires, you describe your pick up location or drop off point using the street name and number as opposed to names of buildings.
Taxi rates and Payment.
For regular taxis and radio taxis, you have to pay in cash.
Uber and Cabify offer credit card payment options.
Currently Uber is still illegal in Argentina, though I recommend taking Uber if available because it's cheaper but don't take Uber from the airport ( Ezeiza) because Uber is not allowed to park right outside the terminals so you'll have to walk for some distance to catch the cab.
Cabify is however legal in Argentina.
Standard taxi rates in Buenos Aires start at $0.78 then $0.07 per 200 meters though rates increase by 20% past 10.00 pm.