Our stay at the Moreno Hotel on the edge of San Telmo was absolutely brilliant and exactly what I needed having spent 2 weeks travelling down from Rio.
Room was huge, clean and extremely stylish. Hotel staff were really helpful and made our stay completely hassle free, giving excellent restaurant recommendations and arranging transfers.
Only downer was the unavailability of the bar and restaurant still being renovated, but this wasn't really an issue with so many great places to eat and drink in BA.
I'd definitely recommend staying at the Moreno, especially if you can get one of the larger loft style rooms.