I would say "Negative Reaction". There is an interview
with Levinson and Link posted on this site saying that they didn't like the idea of expanding the shows to 2 hours because it required unnecessary "padding" to the stories to fill out the time, but the extra scened added here were absolute gems : (1) the scene
with the nun (Joyce Van Patten) and Mr Dolan (Vito Scotti),and (2) the scene with the driving tester Mr Weekly (Larry Storch). Although both scenes could have easily been cut and it wouldn't have effected the story, they are among the most famous classic scenes from the show.
Also we see the gradual change in the relationship between Columbo and Galesko from sympathy growing to one of suspicion, we have Sgt Hoffman (Michael Strong) representing the skeptics in the Police Dept.
Dick Van Dyke, who is primarily a comedy actor was absolutely supberb in this drama (I am surpriseed they
didn't bring him back like they did with Jack Cassidy).
It's all there in this episode which is one of the 2 or 3 best ones.

I think I would choose 'How to dial a murder'. The duel of wits between Columbo and Dr Mason is one of the best in the series.

Another great choice! Good reasons, too.

A great choice and darned good reasons! By the way, do you know if such a course has ever been offered?

I would choose "Negative Reaction." The cemetery scene especially defines what separates the Columbo character from the rest.

Darn good pick! Now if I ask the local community college to offer such a course, I've good choices to offer. I'm a bit surprised--but not disappointed--that Prescription: Murder wasn't mentioned, although the Columbo character was still being "developed" by Falk at that nascent stage.

Michael which one would you pick?

I'd probably stay conservative and go with Prescription: Murder. While I'm tempted to go with a later one from the Golden Age of Columbo, I believe that just about everything's there. A second choice would be Etude, and a third would be Any Port in a Storm. Again, it seems to me that as far as character and plot--Prescription: Murder has the beginnings of it all. (I'd be tempted to have the students chose a later Columbo and write an essay on the similarities between the one they chose and Prescription as an extra credit assignment--they'd have to do it on their own time after the continuing ed. course was over)

Predictably, it would have to be 'Columbo Goes to College' as this is an excellent example of how the great man outmanouvers the 'villans', being that one step ahead.
Also there is of course the relevance to the anticipated audience!!

A good choice!

Candidate for Crime. Holds the record for the most "just one more thing"s in one scene (5 in total.) Jackie Coogan is the perfect paranoid villain who gets let down by his own vanity and Columbo plays the fool very well, slowly enjoying his revelation as a genius at the end.

A Stitich In Crime shows a differebt side to our hero, when Columbo loses the place and bangs the onyx ashtry on the table shouting "I know you did it!"

I be challenged to choose between these two.

I think I'd choose Candidate for Crime for the reasons you've given. In addition, this episode is brimming with topical issues Columbo writers liked to address (Watergate was hitting the front pages at this time).

Though it's in the mid-range of my favs list, Negative Reaction is chockful of clues, Columbo's in classic mode, and Dick Van **** is snarlingly good.

All these picks are terrific....they really are...but I guess we could pick any one of the episodes and find so much "Columboism" in it. Negative Reaction is an excellent one....with Dick VanDyke......(I only mention that one so I can type in the "dyke" part and get away with it!!! )......but really..that episode is a true classic Columbo from beginning to end...as Galesko gets more evil-tempered and annoyed at Columbo.....

Yipes -- I certainly meant no homophobia (that censor filter really is picky -- I'm happy the estimable comedian's first name survived the cut).

I actually was asked years ago by a friend to teach a community college course on mystery films. It fell through, but you should have seen the selection I had ready for those kids.

Well..Martin...you aren't going to leave us in the dark here, are you??? What were your selections? Was it Negative Reaction as you said above...or were there others?

And I think mat also pointed that out about Dick VanDyke....you can say his first name but not his last.