What country has the least brutal, arbitrary police force?

Even in developed (“first world”) countries, police can be vicious thugs who use their power arbitrarily…and get away with it. What country has the least brutal police force? I’d consider factors like the way the police themselves behave, levels of corruption, degree of classism/racism, and how much oversight the police get. Other criteria are welcome too.

Sunshine is the best disinfectant. A country with high levels of oversight might see more brutality reported than one with lax oversight.