Watch out there. Anyone should be very aware of your surroundings in Baires, safety levels vary depending on the neighborhood. For instance, I would not walk alone at night in the "City", the financial hood. I would not walk with a backpack or a bag on a position easy to be taken from you anywhere, not even in tourists tailored areas. And of course, all the standard precautions should be in place (do not wear expensive jewelry, watch, camera, etc).
I am glad you have an amazing experience in Buenos Aires, but as someone who lives for decades in the city, I do not think the differences on security with Brazilian cities are so significant. Yes, it is slightly safer IF YOU STAY IN THE SAFER AREAS.