"Rest in Peace, Mrs. Columbo" was the best ABC years episode and better than most NBC episodes too.
It was a phenomenal story. Sergeant Brady was decent as the sidekick. However, it is Columbo's style to basically work alone. Do not expect many recurring sidekicks.
It would be cool to have a scene in a future episode in which multiple sidekicks of the past appear (A surprise birthday party for the Lieutenant as part of the B-plot, perhaps. This worked wonders on "7th Heaven," the episode in which several people Eric Camden helped over the previous year show up at his surprise birthday party.)