I made the mistake of booking a place online for a month. As others have advised, it is better to rent short term, either a few days in hotel or a week at most in an apartment.
My apartment is fine but extremely noisy due to the traffic (also very bad air due to the car/bus exhaust). This might not bother some people but I really regret booking for a month by internet!
I'd look for a place on a high floor (better air, less noise, more light) or contrafrente (on the back of the building). BsAs is very noisy so finding a quiet apartment is a challenge...
I'm using stayinba.com and they have been good about showing me places for my next month.