Most Americans would name large northern cities like Chicago, NYC and Philadelphia as hotbeds of police corruption. San Fransisco's police force is pretty bad, though. They were just filmed shooting a slowly-walking man a couple months ago, and it wasn't too surprising an incident.
Southern states have corrupt police but tend to be known for using drug trade suspicion to confiscate cash and vehicles from immigrants. This is especially the case in Texas.
Generally, the view of police in any state is dim, though. Only the very smallest/low-density states seem to have few issues that make the news.
