Milhouse is a piece of backpacking industry. Avenue is a big hostel, slightly quieter compared to the sister hostel Hipo, which is more party-oriented. The guests can freely move between the common spaces of both hostels, party in one, sleep in the other one.
There are several features that make Milhouse a good base for exploring Buenos Aires. The hostel organizes walking tours in various parts of the city. The guests can book tickets to events (e.g. a tango show, La Bomba de Tiempo, and many other activities). There is a travel desk at Avenue, good if you will explore Argentina further.
Another cool feature is a stripe-code sticker that you get when you check in. Easy to pay for breakfast and drinks at both Milhouse hostels, perfect during a party.
Some rooms face a patio, some face the street. Mine was towards the street and therefore noisy. One should use ear plugs. The room was shabbish, but ok. The bathroom needs a makeover.