Carla's place is amazing. Much better than the pictures, the view is incredible and the location is great, with proximity to Puerto Madero and San Telmo. We found ourselves walking to many places (we like walking) and rarely took a cab here and there.
Hint: Get coffee and empanadas at the San Telmo fair market (downstairs). Super close by. And check out the "fileteros" of Buenos Aires for something less touristy, a slice of the more traditional culture.