A friend and I stayed at the Art Factory in San Telmo for 3 nights as part of a trip around south America and I can thoroughly recommend it. It is a pleasant hostel around 20mins walk from some of the key tourist spots in Buenos Aires through perfectly safe areas. There is an indoor bar area that is open in the evenings and a nice rooftop terrace too. You're not allowed to bring your own drinks in, but the prices in the bar aren't too bad, though we would have liked them to open a bit earlier, I don't think the bar opens until 5.30pm. The reception staff are helpful and can book taxis (agreed rates for things like airport transfers) and suggest places to visit around Buenos Aires. Entry to the building can be a little tricky, someone at reception has to buzz you in and then you'll have to carry luggage up some stairs with a slightly awkward door. Not a huge issue, but a little inconvenient.
My friend and I shared a private twin room with a shared bathroom immediately across the corridor. The bedroom was fine, plenty of space and quiet at night and even when our nearest bathroom was occupied there are several more fairly nearby.
If/when I ever come back to Buenos Aires I would happily stay here again.