I stayed with Maria and Enrique in Recoleta, a great neighborhood which is safe and has lots of nice restaurants and coffee shops.
They are lovely people and have such a beautiful home. It's 3 or 4 stories and has a private terrace! Everything was charming and clean.
They speak great English and offer advice on what to see and help equip you with subway cards, maps, and anything else you'd need. My last night they woke up very early in the morning and prepared a taxi for me. Throughout my stay they checked-in and made sure I was having a good time and everything was okay.
I would recommend staying with them to anyone. I will stay with them again when I'm in Buenos Aires.