For no real reason at all, I've composed a list of the best television cops in the history of the human race (well, all right...the reason is that I was sick in bed last night and had nothing to do but watch Law & Order and NYPD Blue reruns). The list is limited to cops, as opposed to FBI agents (sorry, Mulder) and government agents (sorry, Kiefer).
1) Andy Sipowicz, NYPD Blue
2) Lennie Briscoe, Law & Order
3) Vic Mackey, The Shield
4) Munch, Homicide
5) Pembleton, Homicide
6) Bobby Simone, NYPD Blue
7) Barney Miller, Barney Miller
8) Columbo, Columbo
9) Hercule Poirot, (technically not a cop, and technically not a part of a television show, just a number of made-for-TV movies based on Agatha Chritie's books. But screw it. I like him.)
10) Mike Logan Law & Order
One of these days, I might expand on my reasoning for ranking them this way; for now, consider this list both authoritative and non-negotiable (I'm looking at you, Benjamin Bratt fans).