I have hear good things about Tamara di Tella-they have branches all over. I think they are fairly expensive-there is another place i used in Recoleta on vicente lopez but i dont have that info right now (name and all) I suggest looking on webindextar.com/ba
I took Tamara Pilates classes when they had a branch on Maure. It was great. I have moved on to others things as form of exercise but I can highly recommend Tamara.