In my experience, the cops in Federal Capital (at least in my old neighborhood) seemed to be decent people... relatively.
There was one who always stood on the corner near my house who I would talk with while waiting for the bus. We got to the level where he told me about his daughters and how they were getting ready to start university and how he was so proud of them. He would also ask me how my studies were going along. Idle chit-chat, but still pleasant enough.
Most of them, if they see you're a foreigner asking for directions, they are pretty helpful. But that's where I draw the line: I would never willingly ask them for anything outside asking for directions.
Now, when I would go visit my friends in provincia (Quilmes, Berazetegui), those cops were a complete disaster. Provincial police are a completely different breed of animal and I wouldn't trust one with the time of day.
In general, we cannot really compare the problems in Argentina with those in the US or Europe. Yes, corruption exists (find me a country where it does not), but corruption has many, many faces and many, many ways of presenting itself. How it is handled is a completely different story and unfortunately, like earlyretirement says, Argentina's system is shot. It functions in anarchy (anarchy in the sense that there is no governing body that forces it to behave and function) and will continue to function this way as long as the people keep being content with that.
I just finished reading a book detailing democracy in Latin America and one of the chapters dealt heavily with Argentina. After the 2001 crash (a perfect time to survey the general population), it was reported that 95% of the people who participated in the survey thought that corruption had gotten worse. This encompassed a wide area ranging from government officials, financial management, and the police. Go figure.
I wonder how the number has changed since that book was published....
