La Boca is probably the most popular neigborhood in Buenos Aires. Humble area where is the famous soccer team Boca Junior where Maradona played. Caminito is very colourfull and full of restaurants and terraces. But La Boca can be a bit dangerous by nigth.
I went there last week and it's beautiful, but there are so many tourists (brazilian most of them) that you feel you are not in Argentina anymore and i think it's not the best place to go if you are in Buenos Aires for a short time.