DNI is wonderful school of Argentine Tango in Bulnes 1011, Buenos Aires. You really can spend all day here. They have a cafeteria and merchandise store on the ground floor, along with the reception area. They also have free wi fi.
They have multiple dance studios on various levels where you can take group and private lessons. There are many teachers and all of them are really good. They also have teachers training programs and practicas. The classes are priced very reasonably and you can also buy a pass. Check their website here.