Here we could get into a dispute about definitions, so at great personal risk I will say this, do you want real tango, or a show, because to me these two things are so diversely different, that I would not even class them as the same dance.

To see real tango you need to see how the locals dance, try Porteño y Bailarin on a Tuesday night Riobamba 345 or El Beso Riobamba 416 Sunday or most nights.If you want to see dancers with a little more space try Salon Dandi on a Wednesday Piedras 936 a few more tourists here but a nice ambiance.
In fact you can find real tango any night of the week, if you name the day I can give you a place to go. If however you want show tango, at the risk of being sniffy, you will have to ask someone else.