The Rockford Files was the best television show from any category, imho. The quintessential private-eye series (the american form of the morality play)! And TV Guide picked Garner as the top television actor of the medium's first 50 years.
I know that in real life, PIs are usually bottom feeders, but in post-expansion American myth they were the avenging angels, the greatest heroes. Then Rockford came along and became the greatest anti-hero.
Was there a longer running PI series? I don't think so.