On the old shows, I think John Bromfield stood out as Sheriff of Cochise and U.S. Marshal.
I saw an interview with his wife and she said that he was much like his TV character. He did most of his own stunts.
I also liked Efrem Zimbalist, Jr. on his FBI show. He was also a PI in 77 Sunset Strip.
BTW, and this is about a real cop...I enjoyed 48 Hours last night, about the Mexican serial killer (Recendez-Ramirez?) who rode trains to commit his many murders. The detective in KY was impressive, but I really liked seeing the Texas Ranger. He was dressed casually, but in the news footage where he took the killer into custody, he was in Ranger garb: that big Stetson, white shirt and tan or gray trousers. (The Rangers are NOT the Highway Patrol. They are an elite investigative unit, also part of the DPS. Sometimes, newscasters and Hollywood get that confused.)
Criminal Minds did a takeoff on this killer, but he didn't sue: he was executed in Texas in 2006. Sometimes, Justice wins. The female prosecutor appeared on 48 Hours and did a superb job of explaining why she was determined to convict and to get a death sentence.