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.
I nearly missed the best free Tango in Buenos Aires, Friday, Saturday and Sunday in Belgrano just get off the train an walk up the hill to the bandstand from 1800 to 2200, La Glorietta, 11 de Sept y Echeverria. On the bandstand itself there will be only dancers but you can stand outside and watch for as long as you like, go off and have a drink some where and just come back again. I love this place, in fact it is the banner on my blog.